Check whether there are sensitive words in the short message content, or send duplicate content to the same number, resulting in being blocked by the operator. You can consult your local operator.
If the mobile phone is in a place where there is no signal or the signal is weak, the message may not be sent successfully. You can try again where the signal is strong.
In addition, the network system is busy, especially during the peak period of holiday information transmission, and faults may occur. It is recommended to avoid the peak period.
If the above methods can't be solved, it is recommended to back up important information, restore factory settings or upgrade the mobile phone system and try again.