Fynex API reference

Fynex Payments API

Accept money and pay it out: hosted checkout, server-to-server card payments, Apple Pay and Google Pay, split payments to marketplace payees, payouts and wallets.

• Rendered documentation /payments-api/v2/docs
• OpenAPI document — generate a client from this /payments-api/v2/openapi.json
• Complete reference as markdown /payments-api/v2/docs.md
• Agent index (llms.txt) /payments-api/v2/llms.txt

Fynex Billing API

Raise and collect the documents that say how much: contracts, subscriptions, metered usage, invoices and credits.

• Rendered documentation /billing-api/v1/docs
• OpenAPI document — generate a client from this /billing-api/v1/openapi.json
• Complete reference as markdown /billing-api/v1/docs.md
• Agent index (llms.txt) /billing-api/v1/llms.txt

Getting a key

One seller secret key authenticates both APIs.

• Where the credential comes from /keys

For coding agents

• What is on this host, and the mistakes to avoid /llms.txt
• Every reference inlined, so an agent needs one request /llms-full.txt
• Task-shaped skills for Claude Code, Cursor and other agent clients /.well-known/skills/index.json