WhatsApp Unavailable Flag

What does the "WhatsApp unavailable" flag mean?

The flag means that a WhatsApp message cannot be sent to a given contact. Contacts marked this way can be filtered in the criteria, similarly to the invalid email address or phone number flag.

A contact's possession of this flag is visible in the Contact Manager module in the contact's preview. 

The flag is given in the process of saving status returns, passed to iPresso after a failed shipping attempt. The contact is flagged when the return has a status of undeliverable or rejected (and the error code for the rejected status is invalidNumber).