Message not sent error keeps appearing on one plus 3t Android 7.0

[AC Question]

Message not sent keeps appearing.

Any suggestions on how to stop?

 

[woutvanheusden]

Try to reboot your phone, first without sim and than again with sim that should work

 

[Gustavo Casas1]

Having same problem I tried both with sim and no sim. I've tried by installing 3rd party apps to deleted the unsent error and still error keeps appearing