How to solve the exclamation point in ipad information?

Ipad information has an exclamation point as follows:

1, the mobile phone information has an exclamation point, which is caused by the failure to send the message. First, we turn on the phone and click the "Settings" system icon.

2. Then we click the "Information" option, as shown below.

3. Then we open the "iMessage" option on the right, close it and restart it.

But to clear the exclamation mark on the message, we need to turn off the Apple mobile phone.

5. Then turn on the Apple phone later. At this point, click the "Information" icon again.

6. Then send the unsent message.