I don’t know what is wrong with my iMessage

Hello franillia,

If you're not able to activate iMessage, these steps may resolve the issue: If you can’t turn on or sign in to iMessage or FaceTime - Apple Support

If you're not able to send or receive messages on your iPhone with iMessage, you may be able to resolve the issue by following the steps here: If you can't send or receive messages on your iPhone or iPad - Apple Support

Thanks.