Error Codes

Errors are returned as { "code": "…", "message": "…" }.

Code	HTTP	Meaning
`notify-invalid-payload`	400	Malformed request body
`notify-template-not-found`	400	None of `templatename` / `templatemap` / `templatepath` resolved to a template
`notify-channel-unknown`	400	The requested channel isn’t mapped to a provider
`notify-recipient-unresolved`	400	The user has no primary channel preference, or no contact value for the channel
`notify-route-all-providers-failed`	400	Every provider for the channel failed; the error `data` lists the providers tried and the last error
`notify-entity-manager-not-found`	500	The tenant’s data engine could not be resolved

Rate limiting: a request that trips an inbound rate-limit class returns 429 with Retry-After. When every provider for a channel is rate-limited, the send result carries status: "rate_limited" and a Retry-After rather than an error.