Payment Gateway Integration for
SaaS: 2026 Playbook

A UK B2B SaaS CTO we worked with in 2025 was scoping payment gateway integration for an enterprise expansion. Existing SaaS used Stripe for small-business customers in the UK and US. New enterprise customers in UK, EU, and APAC needed payment collection via bank transfer (SEPA, Faster Payments, international wires), card payments in multiple currencies, enterprise billing with purchase order workflow, and VAT handling across 11 jurisdictions. Initial engineering plan was BUILD multi-vendor payment integration from scratch: direct integrations with Stripe plus Adyen plus Modulr plus custom VAT engine. Total scope roughly £420k across 10 months.

The honest analysis against business requirements told a different story. Multi-vendor payment integration is exactly what payment orchestration platforms (Spreedly, Primer, Gr4vy, Yuno) exist for; building this from scratch replicated what these vendors deliver as off-the-shelf capability. Subscription billing with enterprise features (purchase orders, custom invoicing, multiple contracts per customer) matches Chargebee or Zuora capability. VAT across 11 jurisdictions is exactly what Merchant of Record providers (Paddle, Lemon Squeezy) or specialist tax providers (Stripe Tax, TaxJar, Avalara) handle.

Revised architecture: ORCHESTRATE Primer as payment orchestration layer routing to Stripe, Adyen, and Modulr by region and payment method; Chargebee for subscription billing with enterprise features; Stripe Tax for VAT calculation; retain existing Stripe integration for small-business tier. Total scope roughly £140k implementation across 5 months, plus Primer monthly fees £4-£8k, Chargebee £800-£1600 monthly, Stripe Tax 0.5 percent per transaction. The CTO's reflection four months after launch: "We launched 5 months faster at one-third the implementation cost. Monthly platform fees are real but much lower than the engineering capacity BUILD would have required for ongoing maintenance. Enterprise customers see our payment capability matching tier-one SaaS competitors. The lesson for any SaaS CTO: do not BUILD what Stripe, Primer, Chargebee, and Stripe Tax do for a living."

That is the payment gateway integration 2026 conversation across UK and US SaaS. Direct integration with Stripe or Adyen or Checkout.com works for single-vendor single-region simplicity. Payment orchestration via Spreedly, Primer, Gr4vy, Yuno works for multi-vendor needs. Embedded via Stripe Elements reduces PCI DSS scope while retaining control. Hosted redirect maximises PCI DSS scope reduction. Subscription billing layer (Stripe Billing, Chargebee, Recurly, Zuora, Paddle, Lemon Squeezy) handles subscription lifecycle distinctly from gateway. Compliance (PCI DSS v4.0.1, PSD2 SCA, 3DS2) and risk (fraud via Stripe Radar/Signifyd/Riskified, chargeback management, tax via Stripe Tax/TaxJar/Avalara) are separate layers.

This article is a practitioner playbook for SaaS CTOs, founders, product managers, and heads of payments scoping payment gateway integration in 2026. The four decision layers. Direct vs orchestration vs embedded vs hosted integration patterns. Subscription billing choice. PCI DSS scope reduction. PSD2 SCA and 3DS2 compliance. Fraud and chargeback management. Honest cost bands. Common failure modes. What we have learned running production payment integrations for 4000-plus TrackVid merchants plus IELTSArena.

The Four Decision Layers of Payment Gateway Integration

Layer 1: Payment gateway vendor selection. The actual payment gateway processing card payments, bank transfers, wallet payments. 2026 UK and global leaders: Stripe (dominant developer-first, strong UK and global), Adyen (enterprise, strong EU/UK), Checkout.com (UK and global enterprise), Braintree (PayPal subsidiary, strong US), Square (SME, strong US), Modulr (UK FinTech focus), GoCardless (Direct Debit and recurring), Worldpay (enterprise), Opayo (UK SME, SagePay heritage), SumUp and Zettle (small business). Selection factors: pricing per transaction, UK coverage, specific payment method support (cards, Pay by Bank, wallets, local methods), geographic coverage, enterprise feature maturity, developer experience.

Layer 2: Integration pattern. How the payment gateway integrates into the SaaS. DIRECT integration via vendor SDK (Stripe SDK, Adyen SDK) delivers full control, lowest fees, highest implementation effort. PAYMENT ORCHESTRATION layer via Spreedly, Primer, Gr4vy, or Yuno routes transactions across multiple gateways based on rules (region, currency, cost, redundancy). EMBEDDED integration via Stripe Elements, Stripe Checkout, Adyen Drop-in, or similar handles sensitive card data in the vendor-hosted iframe reducing PCI DSS scope. HOSTED redirect sends user to vendor-hosted payment page maximising PCI DSS scope reduction.

Layer 3: Subscription billing layer. Distinct from payment gateway. Handles subscription lifecycle (plans, trials, upgrades/downgrades, prorations, dunning for failed payments, revenue recognition, customer self-service). Vendors: Stripe Billing (if already on Stripe), Chargebee (vendor-neutral, strong UK adoption, enterprise features), Recurly (US origins, strong SaaS adoption), Zuora (enterprise), Paddle (Merchant of Record), Lemon Squeezy (Merchant of Record, acquired by Stripe 2024), FastSpring (Merchant of Record). Merchant of Record providers (Paddle, Lemon Squeezy, FastSpring) handle global tax, VAT, compliance by acting as seller of record.

Layer 4: Compliance and risk. PCI DSS v4.0.1 compliance (now mandatory baseline). PSD2 SCA requiring 3DS2 for EU and UK card transactions above £30 unless exempted. 3DS2 (3D Secure 2) authentication. Fraud management via Stripe Radar, Signifyd, Riskified, Sift, Kount. Chargeback management via Stripe Dispute, specialist chargeback providers (Chargebacks911, Midigator). Tax calculation via Stripe Tax, TaxJar, Avalara, Vertex. Each layer requires vendor selection and integration independently.

Per Stripe 2026 payment integration best practices and PCI Security Standards Council v4.0.1 guidance, 2026 SaaS payment gateway integration overwhelmingly uses specialist vendors across these four layers rather than BUILD custom infrastructure; vendor APIs deliver production-grade compliance and operational capability that custom BUILD rarely matches at reasonable TCO.

Direct vs Orchestration vs Embedded vs Hosted Integration Patterns

DIRECT integration via vendor SDK. SaaS integrates directly with payment gateway SDK (Stripe SDK, Adyen SDK, Checkout.com SDK). Full control over checkout experience, lowest per-transaction fees, highest implementation effort, highest PCI DSS scope (card data touches SaaS systems). Best fit: single-gateway single-region SaaS prioritising checkout control.

PAYMENT ORCHESTRATION layer. SaaS integrates with payment orchestration platform (Spreedly, Primer, Gr4vy, Yuno, Payrails, IXOPAY). Orchestration platform integrates with multiple downstream gateways. Routing rules direct transactions to appropriate gateway based on region, currency, cost optimisation, redundancy. Benefits: multi-vendor without multi-vendor integration cost, routing optimisation, vendor comparison, redundancy. Costs: orchestration platform fees (£3k-£25k monthly) plus underlying gateway fees. Best fit: multi-region or multi-vendor SaaS prioritising routing optimisation and redundancy.

EMBEDDED integration via vendor Elements or Drop-in. SaaS embeds vendor-hosted UI components (Stripe Elements, Stripe Checkout, Adyen Drop-in) in own checkout flow. Card data never touches SaaS systems, reducing PCI DSS scope substantially (SAQ A or SAQ A-EP vs SAQ D). Benefits: PCI DSS scope reduction while retaining checkout experience control. Costs: slight checkout UX limitations, vendor styling constraints. Best fit: SaaS prioritising PCI DSS scope reduction without full hosted redirect.

HOSTED redirect. SaaS redirects user to vendor-hosted payment page (Stripe Checkout, PayPal, hosted gateway pages). Card data never touches SaaS systems. Maximum PCI DSS scope reduction (SAQ A). Benefits: minimal PCI DSS compliance burden, fastest implementation. Costs: user leaves SaaS site during payment, less checkout customisation. Best fit: SMEs, high PCI DSS compliance burden avoidance, simple payment flows.

Common failure mode: direct integration when embedded or hosted would suffice. SaaS commits to direct integration for perceived control. Discovers PCI DSS compliance effort (SAQ D requirements including quarterly ASV scans, annual penetration testing, formal security policies) substantially exceeds estimation. Fix: embedded or hosted integration reduces PCI DSS scope to SAQ A or SAQ A-EP with proportionate compliance reduction.

Subscription Billing Layer: Distinct from Payment Gateway

Subscription billing handles subscription lifecycle, distinct from the payment gateway handling transactions.

Stripe Billing. Native integration if already on Stripe. Strong feature set covering subscriptions, trials, upgrades, prorations, dunning, usage-based billing, invoicing. Pricing: 0.4-0.8 percent of recurring revenue plus Stripe transaction fees. Best fit: Stripe-first SaaS with standard subscription patterns.

Chargebee. Vendor-neutral subscription billing supporting multiple payment gateways. Strong UK adoption, enterprise features (purchase orders, custom invoicing, multiple contracts per customer, revenue recognition). Pricing: £300-£1600 monthly plus percentage of transactions. Best fit: multi-gateway SaaS with enterprise billing needs.

Recurly. US origins, strong SaaS adoption, strong subscription analytics. Pricing: 200-800+ monthly plus percentage. Best fit: SaaS prioritising subscription analytics and dunning sophistication.

Zuora. Enterprise subscription billing with strong revenue recognition, complex pricing models, enterprise ERP integration. Pricing: £5k-£30k monthly plus percentage. Best fit: enterprise SaaS with complex pricing and revenue recognition requirements.

Paddle (Merchant of Record). Paddle acts as seller of record handling global tax, VAT, compliance across jurisdictions. Pricing: 5-8 percent per transaction (higher than gateway + billing combined, but tax and compliance included). Best fit: SaaS selling globally wanting tax and compliance simplification.

Lemon Squeezy (Merchant of Record, Stripe-acquired 2024). Similar Merchant of Record model, SME focus. Pricing: 5 percent plus 50 cents per transaction. Best fit: SMEs selling globally.

FastSpring (Merchant of Record). Established Merchant of Record. Best fit: SaaS wanting established Merchant of Record provider.

Choice framework. If primarily on Stripe and standard subscription patterns: Stripe Billing. If multi-gateway or enterprise features needed: Chargebee. If strong subscription analytics priority: Recurly. If enterprise complexity: Zuora. If global tax simplification priority: Paddle or Lemon Squeezy (Merchant of Record).

PCI DSS Scope Reduction Strategies

PCI DSS v4.0.1 is the current mandatory baseline (v4.0 compliance deadline March 2025 passed). SaaS integration pattern materially affects PCI DSS compliance burden.

SAQ D (highest compliance burden). Required when SaaS systems process, store, or transmit card data. Includes quarterly ASV (Approved Scanning Vendor) scans, annual penetration testing, formal information security policies, extensive technical controls, quarterly internal vulnerability scans, QSA attestation often required.

SAQ A-EP (moderate burden). Required when SaaS redirects to payment page but may handle some payment-related functions. Fewer requirements than SAQ D but still substantial.

SAQ A (lowest burden). Required when all cardholder data functions are outsourced to validated third-party service providers. Simplest compliance pathway.

Strategies for PCI DSS scope reduction.

• Embedded integration via Stripe Elements, Stripe Checkout, Adyen Drop-in reduces scope by keeping card data in vendor iframe.

• Hosted redirect to vendor-hosted payment page maximises reduction.

• Tokenisation storing only vendor-issued tokens, never raw card data.

• Network segmentation isolating payment-related systems if direct integration unavoidable.

2026 recommendation. For most SaaS, embedded integration (Stripe Elements, Adyen Drop-in) reduces PCI DSS compliance to SAQ A or SAQ A-EP delivering most of the compliance benefit of hosted redirect while retaining checkout experience control.

PSD2 SCA and 3DS2 for UK and EU

PSD2 SCA (Strong Customer Authentication) requires 3DS2 (3D Secure 2) authentication for EU and UK card transactions above £30 unless exempted.

Exemptions from SCA. Low-value transactions under £30. Low-risk transactions via Transaction Risk Analysis (TRA). Merchant-initiated transactions for subscriptions after initial SCA. Trusted beneficiary (customer-added trusted merchants).

3DS2 implementation. Payment gateways (Stripe, Adyen, Checkout.com) handle 3DS2 implementation. SaaS integration via gateway handles 3DS2 automatically for applicable transactions. 3DS2 reduces false declines versus 3DS1 but still adds friction compared to no authentication.

PSD3 transition. PSD3 expected 2026-2027 UK adoption. Tightens requirements including stronger authentication expectations and clearer Open Banking framework per our fintech API development 2026 piece.

UK Open Banking payments (Pay by Bank). TrueLayer, Tink, Yapily, Volt, Token.io enable account-to-account payments without card networks. Lower fees (typically 0.1-0.5 percent vs 1.5-2.9 percent card), instant settlement via Faster Payments, no chargeback risk, but requires customer bank authentication. Growing in UK SaaS as card alternative especially for larger payments.

Fraud and Chargeback Management

Fraud management vendors 2026.

• Stripe Radar: integrated with Stripe, ML-based fraud detection, good baseline.

• Signifyd: specialist e-commerce fraud with chargeback guarantee.

• Riskified: enterprise e-commerce fraud with chargeback guarantee.

• Sift: fraud and risk platform across industries.

• Kount: Equifax-owned fraud management.

Chargeback management. Dispute response via gateway tools (Stripe Dispute workflow). Specialist chargeback providers (Chargebacks911, Midigator) for high-volume disputes. Prevention through 3DS2 authentication, Address Verification (AVS), CVV checks, velocity checks.

Fraud and chargeback cost reality. Fraud and chargeback losses typically 0.1-1.0 percent of revenue for SaaS depending on segment. Chargeback fees £15-£25 per dispute. Chargeback rate above 0.9 percent triggers card network monitoring programmes with elevated fees. Fraud management investment pays back when fraud and chargeback losses exceed roughly 0.3 percent of revenue.

Tax and Compliance

Tax calculation vendors 2026.

• Stripe Tax: integrated with Stripe, strong coverage, growing feature set.

• TaxJar: US sales tax specialist, broader coverage expanding.

• Avalara: enterprise tax across jurisdictions.

• Vertex: enterprise tax, strong ERP integration.

• Quaderno: EU VAT and global tax SME-focused.

VAT and sales tax reality 2026. UK VAT 20 percent standard. EU VAT varies by country (typically 19-27 percent). US sales tax varies by state and jurisdiction. India GST. Each jurisdiction has registration thresholds and ongoing reporting requirements.

Merchant of Record simplification. Paddle, Lemon Squeezy, FastSpring handle tax calculation, collection, remittance, and reporting as part of their service. SaaS does not need separate tax engine. Higher per-transaction cost (5-8 percent vs 1.5-2.9 percent gateway fees) but tax burden eliminated.

Honest 2026 Cost Bands

Rule that holds. Specialist vendors at each layer deliver production-grade capability that BUILD rarely matches at reasonable TCO; orchestration + specialist subscription billing + Merchant of Record where applicable is the SaaS 2026 default pattern rather than BUILD custom.

Common Failure Modes

Direct integration when embedded would suffice. SaaS commits to direct integration for perceived control. PCI DSS SAQ D compliance effort substantially exceeds estimation. Fix: embedded integration via Stripe Elements or similar reduces to SAQ A or SAQ A-EP.

Not planning subscription billing separately from payment gateway. SaaS builds payment integration without planning subscription lifecycle. Discovers Stripe handles charge but not plan management, trials, prorations. Fix: subscription billing layer (Stripe Billing, Chargebee, Recurly, Zuora, Paddle) scoped as separate layer from day one.

Underestimating PSD2 SCA impact. SaaS integration built pre-SCA then retrofits SCA. 3DS2 authentication flows and exemption handling complexity underestimated. Fix: SCA and 3DS2 scoped from day one for EU and UK transactions.

Ignoring tax complexity. SaaS launches globally without tax engine. Discovers VAT, sales tax, GST compliance burden across jurisdictions. Fix: tax calculation via Stripe Tax, TaxJar, Avalara, or Merchant of Record from day one for multi-jurisdiction SaaS.

Building fraud management when Stripe Radar or similar suffices. SaaS commits BUILD fraud ML. Discovers Stripe Radar baseline plus signifyd layer delivers equivalent or better capability. Fix: baseline fraud management (Stripe Radar), add specialist layer (Signifyd, Riskified) only if fraud losses exceed 0.3 percent of revenue.

Vendor lock-in anxiety overriding orchestration logic. SaaS avoids payment orchestration due to platform fee concerns. Builds multi-gateway integration from scratch adding substantial engineering overhead. Fix: honest TCO comparison; payment orchestration frequently cheaper than DIY multi-gateway at mid-scale.

Not planning for multiple currencies in single-currency SaaS. SaaS launches single-currency, later expands multi-currency, discovers substantial retrofit effort. Fix: multi-currency architecture from day one even if launching single-currency.

Treating chargeback management as reactive. SaaS handles chargebacks reactively per dispute without prevention or systematic response. Fix: 3DS2 authentication plus AVS/CVV plus velocity checks for prevention, dispute response workflow for systematic response.

What We Have Learned Running Payment Integrations for 4000-Plus Merchants

WhiteStone runs production payment integrations across TrackVid (4000-plus Indian ecommerce merchants with payment via Razorpay, Stripe, Shopify Payments, WooCommerce payment plugins, Shiprocket COD), IELTSArena (multi-vendor payment integration serving tens of thousands of students across markets), and various UK and US SaaS payment architecture engagements. Three lessons transfer to any SaaS team scoping payment gateway integration.

TrackVid multi-gateway orchestration pattern delivers 4000-plus merchant payment reliability. TrackVid integrates with Razorpay (dominant India), Stripe (international), Shopify Payments (Shopify merchants), WooCommerce payment plugins (various), and Shiprocket COD workflow. Internal orchestration layer routes merchant payment setup to appropriate gateway based on region, platform, and merchant preference. Vendor-neutral abstraction layer handles gateway specifics. Monthly infrastructure for payment layer under £500 serving 4000-plus merchants; integration pattern supports new gateway addition without architectural change.

IELTSArena multi-vendor payment with jurisdiction-appropriate routing. IELTSArena serves students across markets with payment routed to appropriate vendor by jurisdiction. UK and EU card payments via Stripe with PSD2 SCA handled. Indian payments via Razorpay. Other jurisdictions via Stripe International. PCI DSS scope reduced via embedded Stripe Elements. VAT handled per jurisdiction. Multi-vendor architecture delivered via thin orchestration layer rather than full payment orchestration platform.

UK B2B SaaS CTO case: £140k Primer orchestration plus Chargebee plus Stripe Tax beat £420k BUILD multi-vendor. UK B2B SaaS CTO mentioned above. Honest comparison between BUILD multi-vendor (£420k, 10 months) and ORCHESTRATE Primer plus Chargebee plus Stripe Tax (£140k, 5 months, plus £5-10k monthly platform fees combined). Orchestration delivered better capability per layer at one-third implementation cost and 5 months faster. CTO's lesson: do not BUILD what Stripe, Primer, Chargebee, and Stripe Tax do for a living.

See our portfolio of shipped work for payment integration case studies. For a scoped payment gateway integration assessment, book a SaaS payment architecture call with WhiteStone.

Frequently Asked Questions

What is payment gateway integration and what does it include for SaaS in 2026?

Payment gateway integration for SaaS in 2026 spans four layers: payment gateway vendor (Stripe, Adyen, Checkout.com, Braintree, Modulr), integration pattern (direct, orchestration, embedded, hosted), subscription billing layer (Stripe Billing, Chargebee, Recurly, Zuora, Paddle, Lemon Squeezy), and compliance and risk (PCI DSS v4.0.1, PSD2 SCA, 3DS2, fraud, chargeback, tax). Each layer requires vendor selection and integration independently.

Which payment gateways should SaaS integrate with in 2026?

Dominant 2026 payment gateways: Stripe (developer-first dominant), Adyen (enterprise strong EU/UK), Checkout.com (UK and global enterprise), Braintree (PayPal subsidiary strong US), Square (SME strong US), Modulr (UK FinTech), GoCardless (Direct Debit and recurring), Worldpay (enterprise), Opayo (UK SME). Selection factors: per-transaction pricing, geographic coverage, specific payment method support (cards, Pay by Bank, wallets, local methods), enterprise feature maturity, developer experience.

Direct integration vs payment orchestration: which approach fits SaaS in 2026?

DIRECT integration with single vendor (Stripe, Adyen, Checkout.com) when single payment gateway serves business needs. PAYMENT ORCHESTRATION layer (Spreedly, Primer, Gr4vy, Yuno) when multiple gateways needed for regional coverage, pricing optimisation, redundancy, or vendor comparison. EMBEDDED integration via Stripe Elements or Checkout for PCI DSS scope reduction. HOSTED redirect for maximum PCI DSS scope reduction. Choice depends on multi-vendor needs, PCI DSS priority, and checkout experience requirements.

How does subscription billing integration work in 2026?

Subscription billing is distinct from payment gateway. Payment gateway handles transaction (charge, settle, refund). Subscription billing handles lifecycle (plans, trials, upgrades/downgrades, prorations, dunning, revenue recognition). 2026 vendors: Stripe Billing (if on Stripe), Chargebee (vendor-neutral, strong UK), Recurly (US origins), Zuora (enterprise), Paddle and Lemon Squeezy (Merchant of Record handling global tax). Choice depends on gateway alignment, enterprise feature needs, and global tax strategy.

What are PCI DSS requirements for payment gateway integration in SaaS?

PCI DSS v4.0.1 is current mandatory baseline. SAQ (Self-Assessment Questionnaire) type depends on integration pattern. SAQ D (highest burden) when card data touches SaaS systems. SAQ A-EP (moderate) for embedded integration. SAQ A (lowest) for hosted redirect or fully outsourced card data handling. Embedded integration via Stripe Elements, Adyen Drop-in, or similar reduces scope to SAQ A or SAQ A-EP, delivering most compliance benefit while retaining checkout experience control.

How much does payment gateway integration cost for SaaS in 2026?

Direct Stripe or Checkout.com integration: £20k-£80k implementation plus 1.5-2.9 percent per transaction. Payment orchestration (Spreedly, Primer, Gr4vy, Yuno): £60k-£300k implementation plus £3k-£25k monthly platform fees plus gateway fees. Subscription billing: Stripe Billing £15k-£60k setup plus 0.4-0.8 percent of recurring revenue; Chargebee £20k-£80k plus £300-£1600 monthly; Zuora £120k-£500k plus £5k-£30k monthly. Merchant of Record (Paddle, Lemon Squeezy): £10k-£40k setup plus 5-8 percent per transaction (tax included).

How does PSD2 SCA compliance affect payment gateway integration?

PSD2 SCA (Strong Customer Authentication) requires 3DS2 for EU and UK card transactions above £30 unless exempted (low-value, Transaction Risk Analysis, merchant-initiated for subscriptions, trusted beneficiary). Payment gateways (Stripe, Adyen, Checkout.com) handle 3DS2 implementation; SaaS integration via gateway handles authentication automatically. PSD3 (expected 2026-2027 UK adoption) tightens requirements. UK Open Banking payments (Pay by Bank via TrueLayer, Tink, Yapily, Token.io) growing as card alternative with lower fees.

Which payment orchestration platforms should SaaS evaluate in 2026?

2026 payment orchestration platforms: Primer (strong UK presence, growing enterprise adoption), Spreedly (established US, broad vendor support), Gr4vy (cloud-native, strong feature set), Yuno (Latin America origins expanding), Payrails, IXOPAY. Selection factors: supported gateway integrations, routing rules sophistication, cost (platform fees £3k-£25k monthly typical), observability, enterprise features, geographic coverage.

Why choose WhiteStone Infotech for payment gateway integration?

Transparency note: WhiteStone has not shipped payment gateway integration as a standalone product. Our proof points are direct from production: TrackVid payment integration across Razorpay, Stripe, Shopify Payments, WooCommerce payment plugins, Shiprocket for 4000-plus Indian ecommerce merchants with multi-gateway orchestration pattern; IELTSArena multi-vendor payment with jurisdiction-appropriate routing and PCI DSS scope reduction via embedded Stripe Elements. We delivered a UK B2B SaaS CTO's £140k Primer plus Chargebee plus Stripe Tax orchestration that beat £420k BUILD multi-vendor on both operational outcome and 3-year TCO. Contact WhiteStone Infotech at whitestoneinfotech.com/contact.

The One Thing to Remember

Payment gateway integration for SaaS in 2026 spans four decision layers: payment gateway vendor (Stripe, Adyen, Checkout.com, Braintree, Modulr), integration pattern (direct, orchestration, embedded, hosted), subscription billing (Stripe Billing, Chargebee, Recurly, Zuora, Paddle, Lemon Squeezy), compliance and risk (PCI DSS v4.0.1, PSD2 SCA, 3DS2, fraud, chargeback, tax). Each layer requires vendor selection. Direct integration for single-gateway simplicity. Payment orchestration via Spreedly, Primer, Gr4vy, Yuno for multi-vendor needs. Embedded via Stripe Elements for PCI DSS scope reduction. Hosted redirect for maximum scope reduction. Subscription billing is distinct from payment gateway and often misunderstood. UK B2B SaaS CTO case: £140k Primer plus Chargebee plus Stripe Tax orchestration beat £420k BUILD multi-vendor at 5 months faster. The single decision that determines SaaS payment gateway integration ROI: specialist vendor layers combined through orchestration where multi-vendor needed, or BUILD custom payment infrastructure? Specialist vendor layers at each decision layer deliver production-grade capability that BUILD rarely matches at reasonable TCO.