PaySimple API
PaySimple documents a self-serve REST payments API with a sandbox, HMAC-signed webhooks, and a .NET SDK. Two generations (API 4 and API 5) coexist with different feature sets, so full integrations touch both. Auth is a long-lived plaintext API key; there is no OAuth.
Frequently asked questions
PaySimple scores A on the API Report Card. PaySimple documents a self-serve REST payments API with a sandbox, HMAC-signed webhooks, and a .NET SDK. Two generations (API 4 and API 5) coexist with different feature sets, so full integrations touch both. Auth is a long-lived plaintext API key; there is no OAuth.
PaySimple has a workable official integration path. Most engineering teams can build against it directly. Open API: self-serve, documented, with SDKs
PaySimple is a cloud-based payment acceptance and recurring-billing platform built for service-based small businesses.
Vertical SMB payments, with explicit go-to-market focus on three EverCommerce-aligned segments: Home & Field Services (contractors, HVAC, plumbers, home improvement, maintenance technicians); Healthcare (physician practices, behavioral health, urgent care, with HIPAA-compliant configuration); and Fitness & Wellness (gyms, yoga/pilates studios, salons, spas, med spas, massage therapists, personal trainers). A service business owner signs up for PaySimple (often pushed by their EverCommerce vertical SaaS, e.g., a HVAC contractor on ServiceFusion, a therapist on DrChrono, a salon on SalonBiz), runs a credit check / merchant underwriting, and gets a merchant account with PaySimple as the processor.
Mid-tier within US SMB service-business payments. Latka reports approximately 17,000 paying customers and ~$8M direct ARR for PaySimple itself; EverCommerce reports ~20,000 service professionals on PaySimple and 745,000+ customers across the broader portfolio.
PaySimple holds the AR nervous system for the ~17k-20k SMB service businesses that run on it.
Mature and actively maintained but visibly two-generation. PaySimple launched in 2005 and was acquired by EverCommerce in 2017.
Two coexisting API generations (API 4 legacy + API 5 beta) with non-overlapping feature sets, integrators are explicitly told 'you may need to access both' to ship a complete integration. Authentication uses a long-lived API key passed as plaintext (not Base64) in a `basic` header tied to the merchant account, no OAuth, no scopes, no per-integration key rotation. Full sourced list under Sources below.
Common alternatives include Stripe, Square, PayPal / Braintree, Authorize.net (Visa), Helcim, GoCardless. 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.