iMessage

Try this https://support.apple.com/en-us/HT201422

If it doesn’t work, reset your iPhone to factory settings and start the process again.

Please let me know.

There's a couple things you can try, but don't worry, it happens.

Does your carrier support iMessage? If it's one of the main carriers (ATT TMobile Verizon) it does.

• Try deleting all your messages first
• Make sure time settings are "synced". Open Settings → General → Date & Time and toggle the switch on Set Automatically to ON.
• Make sure iCloud (via your Apple ID on Settings on a Mac has the Messages checkbox "ON".
• Restart the iPhone and make sure you have a good wifi or carrier connection.

Try this and let me know.

On your iPhone, go to Settings and Messages. Toggle the button for iMessage.

Let me know how it goes.