validation_error

Status: 422 · Code: validation_error

The request shape was understood, but one or more fields didn't pass validation. The response includes an errors array with per-field details.

{
  "error": {
    "code": "validation_error",
    "message": "Request validation failed. Check 'errors' for details.",
    "status": 422,
    "errors": [
      { "param": "to", "code": "too_many_recipients", "message": "Maximum 50 recipients allowed." },
      { "param": "subject", "code": "required", "message": "Subject is required." }
    ]
  }
}

How to fix

Always inspect the errors array — not the top-level message. Each entry has:

• param — which field failed
• code — stable machine-readable reason (required, too_long, invalid_format, too_many_recipients, etc.)
• message — human-readable summary

Fix every entry, not just the first — we return all failures at once so you can fix them in one pass.

Related

• Error handling
• sender_not_verified
• too_many_recipients