The HTTP status 402 may occur when trying to send an email using the Send a Message endpoint. The mail provider may reject the message because of its content or recipients. If the message includes
Sending to at least one recipient failed or
Sending to all recipients failed, your message hasn't been delivered to some or all of the recipients.
Confirm all email addresses are valid. If any of the recipient addresses contain non-ASCII characters such as characters with accents or other symbols, these deliveries will fail.