When sending a text message, the mobile phone prompt was sent successfully long after it was sent.

it's been a long time since the news reported that the other party may have turned off the phone, but it seems that your problem is not like this. There is also a bad signal, which is of course the most likely.

if the message report fails, if the other party has not stopped, it is because the SMS set by your mobile phone has expired. That is to say, if your short message is valid for 6 hours, if it is not sent successfully within 6 hours, you will receive a message report of sending failure, and this validity period is generally set to the maximum. What I said is a little messy. I don't know if you understand. I hope I can help you.