Why can't oppo mobile phones send messages?

Check with reference to the following methods:

1, and confirm whether the number of the SMS center is correct;

2. The network congestion of the operator's base station leads to the delay of receiving short messages;

3. The memory of the receiver's mobile phone is full;

4. The receiver's mobile phone is not turned on for a long time or is not in the service area, and the message is deleted by the SMS center after overtime;

5, there are sensitive words, which have been directly deleted by mobile or Unicom in the SMS center.