Send failed

A send run could not complete and the article was parked in failed, alongside the human-readable failure_reason this payload carries.

Refusals that happen before dispatch starts, such as an unverified sender or a billing gate, are rejected synchronously when the send is requested and never reach this topic. What lands here is a run that began and then broke, most commonly every delivery failing at the provider.

Delivered as a single HTTPS POST to the consumer's registered endpoint, with the message as the JSON request body. Respond 2xx to acknowledge. Anything else, or a timeout, is retried with backoff, so acknowledge fast and do the work afterwards.