Sign Out And Back In To iMessage

1. Open the Settings app.
2. Tap Messages.
3. Tap Send & Receive.
4. Tap your Apple ID at the top of your iPhone’s display.
5. Tap Sign Out.
6. To sign back in, tap Use your Apple ID for iMessage.
7. Enter your Apple ID (if necessary) and Apple ID Password.
8. Tap Sign In.

Why this works:

Signing out and back into iMessage has the potential to fix any technical issues that may have been interrupting your iCloud account’s ability to send and receive iMessages. From this screen, you can also log into a different iCloud account if the account your currently signed into is old.