Imessage Error
I am getting the error message "An errror occurred during activation. Try again." Everytime I try to turn imessage on. I've tried all the solutions on apple support site and still nothing has changed.
iPhone 13, iOS 15
If you followed all of the steps in the Related Article listed in your post, then the final step in that is to contact Apple Support. Use the Get Support link at the top of the page here to do that.