Hello, my iMessage is not working. Can you please help me fix it?

If Messages has been working ok, and has stopped working:

Try restarting your iPhone, as that often restores order.

How to: Restart your iPhone

Else:

If you need to set-up Messages to use on an iPhone:

How to: Set up Messages

How to: Send and reply to messages

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Trouble-shooting: What to do ... if ...

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

or

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

or

If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support

If you still need help:

If you want, you can contact Apple Messages Support:

There is a link to Support staff at bottom right on the webpage that opens from the link below.

Messages for iPhone, iPad, Apple Watch, and Mac - Official Apple Support

All the best :-)