Why can't I send a message when my SMS center number is correct? I am Unicom card

First, check whether the mobile phone status is normal and whether the SMS sending and receiving function is turned on. Secondly, check whether the number of the SMS center is set correctly (generally, the number of the SMS center is set in the mobile phone settings, but each model is different, so it is recommended to set it according to the manual of the mobile phone). Then, check whether the SMS message box is full, and suggest clearing the message. Finally, you can't send text messages after the above investigation. It is suggested to contact the manual desk to handle or consult the business office at that time.