Errors

Every non-2xx response shares this shape:

{
  "error": "QuotaExceeded",
  "message": "Monthly email limit of 1500 reached and only 0 credit(s) remain. Buy more credits or upgrade your plan to continue sending."
}

Validation errors additionally include a details array with per-field messages. Quota errors include a usage object:

{
  "error": "QuotaExceeded",
  "message": "Monthly email limit of 1500 reached and only 0 credit(s) remain...",
  "usage": {
    "sent": 1500,
    "limit": 1500,
    "credits": 0,
    "needed": 1
  }
}

Error codes

Status	Error	When
400	Validation Error	Request body failed schema validation (e.g. invalid email address, missing required field).
400	InvalidAttachment	An attachment is too large, is a blocked file type, isn’t valid base64, or its path couldn’t be downloaded.
400	InvalidJSON	The request body isn’t valid JSON — most often raw file bytes sent where base64 was expected.
413	PayloadTooLarge	The whole request body exceeded the size cap. Send fewer or smaller attachments, or pass a path instead.
401	Unauthorized	Missing, invalid, or revoked API key.
403	Forbidden	The from domain isn’t verified yet, or the account is suspended.
404	Not Found	The resource (email, domain, API key) doesn’t exist or isn’t yours.
409	Conflict	Domain already registered on this or another account.
429	QuotaExceeded	Monthly plan quota and any purchased credits are both exhausted.
429	DailyQuotaExceeded	Free plan’s 150 emails/day cap reached.
502	Email Send Failed	The email provider rejected the send after your request passed all cmdsend-side checks.