MX Platform API vs Teller

MX Platform API

Three public OpenAPI files, llms.txt, Markdown docs and a written version policy with 18 months of support and Deprecation and Sunset response headers. No price, client agreement or SLA is published, production keys need MX's approval, every calling IP address must be allowlisted, and the status page records three platform-wide error incidents since 10 July 2026.

Teller

Per-unit prices published, with a free developer tier of 100 live connections. US only.

MX Platform API

1. Send Accept: application/json, Accept-Version: v20260929 and Basic auth of client_id:api_key on every call. A missing version returns 406
2. Ask the owner to allowlist the calling machine's static IP in the Client Dashboard first. Other addresses get 403, and some failed authentication returns 404
3. Test against https://int-api.mx.com with institution mxbank, username mxuser and any password. It has no aggregation throttle
4. Set your own id when creating users and members. A repeat returns 409, which makes a retried create safe
5. Expect 202 without an error when a standard aggregation is throttled (three hours by default). Balance checks stop at 5 per member every 2 hours with 429
6. Pass includes[]=merchant or includes[]=category as an array on transaction lists. A comma-separated string returns 400

Teller

1. In sandbox call https://api.teller.io/accounts with -u "$TELLER_ACCESS_TOKEN:" and no certificate; add the client certificate only for development and production
2. On a 404 enrollment.disconnected.* code, stop and send the user back through Teller Connect in update mode; retrying won't help
3. Pin the Teller-Version header so a dashboard upgrade doesn't change response shapes under you
4. Widen transaction syncs 7 to 10 days past the last sync to catch pending items that change date
5. Send an Idempotency-Key on every payment request; keys are kept for 72 hours