Whatsapp will reject messages with 1210 if the messages are sent with a Whatsapp Business number that is in Restricted status. They are rejected because there are restrictions on how many messages can be sent from this phone number. This may be because too many previous messages were blocked or flagged as spam. During a Restricted phase, customers can not send any notification messages until the 24-hour window has been reset. However, customers can still respond to the messages that were initiated before.
Customers can have restrictions placed on their numbers by WhatsApp if they are blocked or flagged too much by their end-users. This is a WhatsApp automated system that we have no control over.
When this error occurs, customers would have to ensure they revisit the content of the messages. It is recommended to check if any new template was added within the last seven days. This may help determine a problematic template(s). It would also help if the end-users opt-in for any recent template topics. For example, if the users had opt-in only for purchase receipts but not for the account updates, customers may respond negatively because they didn't opt into that specific communication. It is recommended not to initiate any new messages through the restricted number for the next 24 hours. Customers with multiple Business Numbers can choose to send the traffic using the other numbers.