What Is a Payment API for ISVs?

A payment API is the technical bridge that connects an independent software vendor's (ISV) platform to payment processing infrastructure — enabling card acceptance, ACH, tokenization, settlement, and reporting without redirecting users to a third-party portal. For ISVs, the API is the front door. But as the industry has matured, what lives behind that door matters far more than how clean the doorknob looks.

Why Payment Integration Is Now a Strategic Imperative

Embedded payments are no longer a product differentiator — they're table stakes. Revenue opportunities for software platforms embedding payments are projected to surpass $51 billion by 2026, up from $21 billion in 2021 (Bain & Company). ISVs that still route users to external processors are leaving recurring revenue, platform stickiness, and competitive positioning on the table.

The case is clear:

Revenue: ISVs can earn a share of every transaction processed within their platform.

Retention: Platforms that embed payments see lower churn because switching costs increase.

Valuation: Native payments functionality increases the attractiveness of an ISV for acquisition or investment.

Can our team go from zero to processing a test transaction in under a day?

The 7 Criteria U.S. ISVs Should Use to Evaluate Payment APIs & SDKs

1. Integration Speed and Developer Experience

Time-to-market is critical. Evaluate: How clean is the API documentation? Are SDKs available in your stack's languages (Python, Node.js, Java, C#)? Is there a sandbox environment that returns real responses rather than mocked data? Look for OpenAPI specs, Postman collections, GitHub repos, and interactive demos — signals that a provider is genuinely developer-first.

What to ask: Can our team go from zero to processing a test transaction in under a day?

2. PayFac and Sub-Merchant Architecture

PayFac-as-a-Service allows ISVs to onboard merchants under a master account, dramatically reducing merchant friction. Evaluate whether the provider offers a Merchant Boarding API so onboarding can be embedded directly into your UI — rather than requiring merchants to complete a separate application process. The best partners reduce a weeks-long process to minutes.

What to ask: Does the provider offer a sub-merchant boarding API, and who carries the underwriting liability?

3. Revenue Share and Monetization Structure

The most undervalued criterion in early-stage evaluations. ISVs should ask not just whether revenue share exists, but how it's structured: per-transaction basis points, markup on interchange, or a hybrid? Transparent, contractually defined revenue share — not verbal promises — is what separates real partners from vendors.

What to ask: Can we see a projected revenue model based on our current or anticipated processing volume?

4. Payment Method Breadth

U.S. merchants increasingly need more than Visa/Mastercard. Evaluate support for: ACH/eCheck, digital wallets (Apple Pay, Google Pay), BNPL, recurring billing, virtual terminals, and invoicing. For card-present ISVs, certified hardware and semi-integrated terminal APIs (PAX, Ingenico, etc.) matter as much as the software stack.

What to ask: What payment types are supported natively versus via third-party add-on?

5. Compliance Coverage (PCI, KYC, AML)

Compliance is where integrations stall and relationships break down. A payment partner should provide end-to-end PCI DSS coverage, built-in KYC/AML tooling for sub-merchant onboarding, and point-to-point encryption (P2PE) for card-present scenarios. The ISV should understand exactly where its compliance scope begins and ends.

What to ask: What is our PCI scope under this integration model, and what do you certify?

6. Support Quality and Integration Enablement

APIs win demos. Enablement wins partnerships. What happens when an integration stalls at 11pm the night before go-live? Dedicated integration engineers, single points of contact with authority, and post-launch relationship management are not soft benefits — they are core product features for ISVs. Slow support damages the ISV's reputation with their own merchants.

What to ask: Who is our dedicated integration contact, and what is your SLA for technical escalations?

7. Pricing Transparency

Hidden fees erode ISV revenue sharing and surprise merchants. Evaluate: Is pricing interchange-plus or flat-rate? Are there monthly minimums, PCI non-compliance fees, chargeback fees, or early termination penalties buried in the contract? Clear, published pricing or a written fee schedule before signing is non-negotiable.

What to ask: Provide a written breakdown of every fee we or our merchants could encounter.

The Bottom Line

When U.S. ISVs evaluate payment APIs and SDKs, the checklist goes well beyond documentation quality. The real evaluation is about the partner model: Who carries compliance burden? Who shows up when the integration stalls? Who is structured to help you earn — not just process?

APIs create the first impression. Enablement, economics, and partnership create the long-term outcome.

For ISVs building embedded payments for U.S. merchants, Payarc is built specifically for this use case — from its PayFac infrastructure and transparent revenue share to its AI-native risk suite and white-glove integration support.

Frequently Asked Questions

What is the difference between a payment API and an SDK for ISVs?

A payment API is the set of endpoints that allow your platform to send and receive payment data — authorizing transactions, retrieving records, managing sub-merchants. An SDK (Software Development Kit) is a pre-packaged set of tools, libraries, and code examples that makes calling those APIs easier within your specific programming language or framework. Most embedded payments providers offer both. The SDK reduces integration time; the API provides the flexibility for custom workflows.

What is PayFac-as-a-Service and do ISVs need it?

PayFac-as-a-Service allows an ISV to onboard merchants as sub-merchants under a master merchant account — without becoming a registered Payment Facilitator itself. This eliminates months of regulatory work and capital requirements while still enabling the ISV to control the payments experience and earn revenue share. Most growth-stage ISVs benefit from a PayFac-as-a-Service model over a direct referral arrangement.

How do ISVs make money from embedded payments?

Primarily through revenue share — earning a portion of the interchange or margin on each transaction processed through their platform. Depending on the provider and volume, this can range from a few basis points to 100bps (1%) or more per transaction. At scale, this becomes a significant recurring revenue stream that compounds with the ISV's merchant base growth.

How long does a payment API integration take?

Depends heavily on the provider's documentation quality, sandbox environment, and dedicated support. With a well-resourced provider and a dedicated integration engineer, most ISVs can complete a standard integration in 2–4 weeks. Complex custom builds with hardware and multi-payment-method support can take 6–12 weeks.

Is Stripe a good fit for U.S. ISVs seeking revenue share?

Stripe is a strong option for developer experience and global coverage. However, its ISV revenue sharing model is limited compared to processor-direct or PayFac-as-a-Service providers. ISVs prioritizing monetization should compare Stripe's economics carefully against providers like Payarc, Finix, or North before committing.