Once you do this, you can re-open the iMessage app on your iPhone and try sending a message to a chosen contact. If your problem is solved, then great. However, if you are still unable to solve the issue, the only solution is to head to the service center and allow their technicians to take a look. Sometimes, it’s an Apple Account issue, which they help you rectify easily.
Please ensure that you get the issue rectified as soon as possible, since iMessage is the only default SMS app you have on the iPhone, and you will need it working to full effect in order to make transactions or even verify your details using SMS verifications.
