I am unable to activate iMessage on my iPhone

Re: "iMessage: when i try to select my phone number on IMessage i get a notfication ‘

"an error occurred during activation’’ i couldn’t fix it.

i did everything mentioned on the websites. Need help please".

If you are new to Messages:

How to: Set up Messages on iPhone - Apple Support

or

What to do: 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 - Apple Support

Also:

How to: Add or remove your phone number in Messages or FaceTime - Apple Support

If needed:

Apple Messages Support website (info. / support / contact)

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