iMessage on my iPhone is not working

Commiserations!

See if anything in these articles can help:

If you have an issue with Messages or FaceTime after setting up your new iPhone - Apple Support

or

Try following the steps in Apple Support's article:

If you can’t turn on or sign in to iMessage or FaceTime - Apple Support

If more help is still needed:

If you can't send or receive messages on your iPhone or iPad - Apple Support

or

See if this discussion thread on a similar topic helps you:

Why is my iMessage not working - Apple Community

If needed:

iPhone Support Team have a "Get Support" link at the bottom of their website (link below)

iPhone - Official Apple Support

or

There's a web-form available for sending feedback on the Messages app

They likely won't reply, but it will reach those who can make changes in future updates.

iPhone /  iPad:   

Feedback - Messages for iOS and iPadOS - Apple

Mac OS.    Feedback - Messages - Apple

All the best :-)