When webhooks fail (HTTP codes)

Read webhook delivery errors and fix the most common integration mistakes.

Last reviewed: 2026-05-07

Typical outcomes:

401 / 403 — Wrong API key, missing header, or IP allowlist on your side.
404 — URL path changed; update the webhook target.
422 / 400 — Schema mismatch; confirm you picked the correct adapter (Klaviyo vs generic JSON).
429 — Your ESP throttled fanmigo; retry later or raise limits with the provider.
5xx — Provider outage or bug; fanmigo will retry according to internal rules; fix server errors on endpoints you host yourself.

After changing credentials, always run Test again. For persistent failures, copy the response body from your ESP logs (redact secrets) when contacting support.