Guides

Errors

Every error has the same shape, with a code that never changes meaning. Branch on the code; show the message.

409 Conflict

{
  "error": {
    "code": "conflict",
    "message": "This campaign is already sending"
  }
}

The message names the field when the input is wrong, and says what to do when a rule stops the action. MCP tools answer the same object in an error result. Sending a campaign that is already sending or sent answers conflict, so a retried send never goes out twice.

Code	Status	Meaning
`unauthorized` The API key is missing, malformed, unknown or revoked.	401	The API key is missing, malformed, unknown or revoked.
`forbidden` The key's level doesn't allow this action: a signups only key can only add contacts.	403	The key's level doesn't allow this action: a signups only key can only add contacts.
`not_found` The newsletter, campaign, contact, domain or key isn't in this account.	404	The newsletter, campaign, contact, domain or key isn't in this account.
`validation_failed` The input doesn't match the schema or breaks a rule. The message names the field.	400	The input doesn't match the schema or breaks a rule. The message names the field.
`conflict` The resource's state doesn't allow it, e.g. sending a campaign that is already sending or sent. Retrying won't help.	409	The resource's state doesn't allow it, e.g. sending a campaign that is already sending or sent. Retrying won't help.
`rate_limited` Too many requests with this key. Wait a minute and retry.	429	Too many requests with this key. Wait a minute and retry.
`subscription_required` The account has no active plan.	402	The account has no active plan.
`billing_off` The server is self-hosted without billing: every account has every feature, without plan limits.	404	The server is self-hosted without billing: every account has every feature, without plan limits.
`plan_limit_emails` The send needs more emails than the plan has left this month.	402	The send needs more emails than the plan has left this month.
`plan_limit_subscribers` The account has more active subscribers than its plan allows.	402	The account has more active subscribers than its plan allows.
`account_blocked` The account is blocked after spam signals (bounce or complaint rates, a spam trap, the email provider) or by an admin. Nothing is sent, and only reads, pausing, unscheduling, revoking access and billing work until an admin unblocks it.	403	The account is blocked after spam signals (bounce or complaint rates, a spam trap, the email provider) or by an admin. Nothing is sent, and only reads, pausing, unscheduling, revoking access and billing work until an admin unblocks it.
`sender_not_allowed` The from address is neither the newsletter's shared address nor on a verified domain of this account.	422	The from address is neither the newsletter's shared address nor on a verified domain of this account.
`send_check_failed` A pre-send check failed: no postal address, subject or content, or the email is over 100 KB.	422	A pre-send check failed: no postal address, subject or content, or the email is over 100 KB.
`no_recipients` Nobody is left to send to.	422	Nobody is left to send to.
`sending_disabled` Sending is turned off on this server.	503	Sending is turned off on this server.
`unavailable` A service the action needs isn't configured or didn't answer. Retry later.	503	A service the action needs isn't configured or didn't answer. Retry later.
`internal_error` Something failed on MailCheap's side.	500	Something failed on MailCheap's side.