Why can't text messages for the senior high school entrance examination always be sent out?

One of the common reasons why text messages can't be sent out is the arrears of mobile phones.

It's normal that you can't send text messages because your mobile phone is in arrears. If this is the case, you can call the operator's customer service phone to check the phone bill balance. If it is confirmed that the phone bill is insufficient to recharge, you can send a short message immediately.

If the signal is not good, sending SMS will fail. Try to send it to another place (as empty as possible, preferably where there is no obstruction).