Payment API Integration for Software
Technical guide to payment API integration for software companies — architecture patterns, SDK options, and choosing the right API approach for your ISV.
Payment API integration is the technical foundation of embedded payments. The APIs you choose — and how you architect around them — determine your platform’s payment capabilities, PCI scope, and long-term flexibility.
API Integration Patterns for ISVs
Hosted Fields / Drop-in Components
The payment provider’s pre-built UI components render inside your application. Card data goes directly to the provider — never touching your servers. Lowest PCI burden (SAQ A). Used by most ISVs.
Server-Side API
Your backend sends payment data directly to the provider’s API. Maximum flexibility but requires SAQ D PCI compliance. Only appropriate for ISVs with dedicated security teams.
Payment Orchestration
A middleware layer (Spreedly, Nexio) that abstracts multiple processor APIs behind a single integration. Enables multi-processor routing without building separate integrations.
What ISVs Should Evaluate in a Payment API
- SDK quality: Language-specific SDKs, type definitions, error handling
- Documentation: Interactive examples, guides, changelog transparency
- Sandbox: Realistic test environment with simulated declines, disputes
- Webhooks: Reliability, retry logic, event types covered
- Versioning: Backwards compatibility, migration guides for breaking changes
- Rate limits: Whether your platform’s volume fits within API constraints
Common Integration Mistakes
- Starting with server-side when hosted fields would suffice — unnecessary PCI complexity
- Not implementing idempotency — duplicate charges from network retries
- Ignoring webhook reliability — missed settlement or chargeback notifications
- Hardcoding to one processor — makes future migration expensive
Build your payment architecture with portability in mind. Abstract the provider-specific layer so you can switch processors without rewriting your entire payment flow.