I used the Unicom number, and the mobile phone showed that the short message was sent successfully but the other party didn't receive it. What happened?

The reasons why the message was sent successfully but not received by the other party are as follows:

1) Because the receiver's memory is full, you can delete redundant messages.

2) The receiver's signal is poor, so users can be advised to send it to a place with better signal.

3) It is related to the processing capacity of the SMS center, which may be due to congestion, packet loss or interconnection barriers.

4) The user has not enabled the SMS function (under normal circumstances, the user will automatically enable this function after accessing the network).