Why are all my emails sent via API failing? | Zoho CPaaS

Why are my emails sent via API failing?

There are several reasons for email-sending failures. The prominent ones are listed below:
  1. One or more mandatory fields - "subject", "from", "to", "cc", "bcc", "reply_to" were set as an Empty Value or Invalid Value.
  2. The email-sending domain is unverified.
  3. The Zoho CPaaS account is yet to be reviewed by us.
  4. The JSON used is malformed. Ensure the JSON is well-formatted.
  5. If you are using a template key or alias, ensure their values are correct. 
  6. The generated send mail token is invalid.
  7. Invalid file cache key.
  8. Fields exceeding limits:
    1. reply_to <= 40
    2. to <= 340
    3. cc <= 100
    4. bcc <= 100
    5. Character limit (<=250) exceeded for the name field for any of these parameters - from, to, reply_to, cc, bcc.
    6. Subject field exceeding the character limit (<=500).
    7. Attachment filename exceeding the character limit (<=150).
    8. Attachment size exceeding the limit (<=15 MB).
    9. Number of attachments used exceeding their limit (<=60).
Refer to our help guide here that lists the error codes and solution for each error.

If you are still facing difficulties with troubleshooting, write to support@zohocpaas.com with a screenshot of the error.