> ## Documentation Index
> Fetch the complete documentation index at: https://docs.apollodeploy.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Troubleshoot send and cancellation errors

> Map email operation status codes to the customer state that must be corrected

Start with the HTTP status and structured problem response.
Then confirm the authenticated project, request shape, domain, recipient state, and current usage.

## Send-email responses

| Status | Verified meaning                        | First checks                                                                         |
| ------ | --------------------------------------- | ------------------------------------------------------------------------------------ |
| `201`  | Request accepted                        | Follow the returned message status; this is not delivery proof                       |
| `400`  | Invalid request                         | Required fields, email syntax, body presence, schedule, attachments, recipient shape |
| `401`  | Invalid or expired credential           | Authorization value, key status, expiry, project binding                             |
| `403`  | Permission or project access denied     | Required permission and authenticated project                                        |
| `413`  | Resolved audience exceeds 50 recipients | Topic or segment size; split through an authorized workflow                          |
| `422`  | Valid shape but send cannot proceed     | Verified From domain, active project, resolved audience, sending state               |
| `429`  | Endpoint or abuse-control limit applied | `Retry-After`, request rate, live Usage page                                         |

The send endpoint requires `from`, `to`, and `subject` plus at least one of `html` or `text`.
An audience ID must be the only `to` value and cannot be combined with `cc` or `bcc`.

## Cancellation responses

A single-message cancellation succeeds only while the record is `scheduled`.
If dispatch already began, Signal returns a conflict rather than claiming the message was cancelled.
The bulk cancellation operation affects messages that are currently scheduled; it does not recall messages already handed off.

## Structured problems

Capture the response's problem type, title, status, detail, and structured fields.
Do not reduce every failure to the HTTP reason phrase; the problem body identifies the relevant customer condition.

## Before retrying

* Correct `400`, `401`, `403`, `413`, and `422` conditions first.
* For `429`, honor `Retry-After` and use bounded backoff.
* Preserve the same body `idempotencyKey` for the same logical send.
* Do not automatically resend bounced, complained, unsubscribed, or suppressed recipients.
* For `indeterminate`, inspect the existing record before creating any new send.

## Evidence for support

Provide the Signal email ID, UTC timestamp, endpoint, HTTP status, problem type, and project identifier.
Redact API keys, Authorization headers, recipient content, and attachment data.

<Card title="API errors" icon="circle-exclamation" href="/signal/api-reference/errors">
  Review the shared problem format and status-code behavior.
</Card>