FreeAgent API vs Rutter Accounting API

FreeAgent API

Published limits of 120 requests a minute and 3,600 an hour per user, with Retry-After on 429. No OAuth scopes, so a token can do anything the authorising user can.

Rutter Accounting API

Idempotency-Key header on writes, and prefer_sync writes that fall back to async after 30 seconds. Production prices are quote-only.

FreeAgent API

1. Store the new refresh token from every refresh response. The old one stops working
2. Create the invoice, then PUT /v2/invoices/:id/transitions/mark_as_sent. A draft isn't visible to the customer
3. Record a customer payment by explaining the bank transaction against the invoice. There's no invoice payments endpoint
4. Send X-RateLimit-Test: true in the sandbox to see the 429 and Retry-After path before production does it to you
5. Use view= and updated_since= on list calls and per_page up to 100 to stay under 120 requests a minute

Rutter Accounting API

1. Send X-Rutter-Version: 2024-08-31 on every call
2. Send an Idempotency-Key on every create so a retry after a timeout doesn't write twice
3. Use response_mode=prefer_sync and handle the 202 async_response anyway
4. Treat 452 as the ledger throttling you and 429 as Rutter's 500-per-10-seconds organisation limit
5. Keep access_token out of logged URLs. The docs only show it as a query parameter