Sending text messages to mobile phone numbers always fails. Called and said it was turned off. What happened?

If the customer sends a short message to a mobile phone number, but the feedback information of the system cannot be sent after a period of time, the following aspects can be considered: dial the number to prompt the shutdown:

If sending to a certain number fails, other numbers can be sent normally, which means that the other number is turned off for a certain period of time, and it is not the customer's mobile phone problem that can't receive this short message normally.

After sending a short message to the other party's number, after the time specified by the system has passed, the other party's number has not been turned on to receive this short message, and the system will feedback to the sending number that "sending failed".

Reminder: As the rules set by different operator systems are inconsistent, the time specified by the specific system shall be subject to the regulations of each operator.