Stax API
Stax runs a self-serve REST API at docs.staxpayments.com covering payments, customers, invoices, subscriptions, terminal charges, and webhooks, with merchant and partner API keys. The Stax Connect partner program requires a contract; back-end SDKs beyond mobile and JavaScript are missing.
Frequently asked questions
Stax scores A on the API Report Card. Stax runs a self-serve REST API at docs.staxpayments.com covering payments, customers, invoices, subscriptions, terminal charges, and webhooks, with merchant and partner API keys. The Stax Connect partner program requires a contract; back-end SDKs beyond mobile and JavaScript are missing.
Stax has a workable official integration path. Most engineering teams can build against it directly. Open API: self-serve, documented, with SDKs
Stax is an Orlando, Florida-based payment processing and billing software company founded in July 2014 by sibling co-founders Suneera Madhani and Sal Rehmetullah under the original brand Fattmerchant, rebranded to Stax in 2021.
Vertical: Financial Services (payment processing, embedded payments, subscription billing). In-person card acceptance: Stax POS app on iOS/Android, Stax-branded terminals, Tap to Pay on iPhone for retail, healthcare front desk, legal/professional services and field-service checkout..
Medium in the SMB processing tier; low in the developer/ISV community. Stax has publicly cited tens of thousands of merchant accounts across the combined Stax + Payment Depot + Stax Connect partner footprint, with named ISV partners across vertical SaaS.
Stax handles a comprehensive merchant-services and subscription-billing data set on behalf of its SMB and ISV customers: Payment instruments: card PANs, expiry, CVV (transient), bank account/routing numbers for ACH, tokenized card and bank methods stored in the Stax vault, wallet tokens (Apple Pay, Google Pay, Tap to Pay on iPhone)..
Founded July 2014 as Fattmerchant in Orlando, Florida by Suneera Madhani and Sal Rehmetullah; rebranded to Stax in 2021; ~12 years old as of 2026.
Limited first-party back-end SDKs (Android, iOS, JavaScript only; Python referenced but thin), Go, Ruby, PHP, .NET and Node back-end integrators hand-roll HTTP clients vs. Stripe's broad SDK matrix. Stax Connect (the embedded-payments / partner API) requires a partner-program contract and revenue-share negotiation rather than self-serve sign-up, meaningful friction for ISVs that want to evaluate before committing. Full sourced list under Sources below.
Common alternatives include Stripe, Square (Block), PayPal / Braintree, Helcim, Payment Depot (Stax-owned sibling brand), Clover (Fiserv). Graded alternatives appear under "More from the report card" below.
Grades measure one thing: can a customer's engineering team get their own data out programmatically? We check six things (whether a real API exists, how access is gated, data coverage, auth quality, docs and developer experience, and stability) and roll them into a letter grade. Grades get re-verified, and they only move on evidence.