My iMessages is not activating

Ran into the same issue today but figured out a way of fixing the issue.

My new phone plan has 5G availability where previously I only had LTE. Under the Cellular settings, it was pointing to "5G Auto".

FIX: I temporarily set it to connect to LTE and then tried activating the iMessage and FaceTime again. After this resolved the iMessage activation issue, I switched back to 5G Auto without it reverting back the activation issue.

Hey there,

To use iMessage or FaceTime, you need to activate them on your iPhone, iPad, or iPod touch. If you see an error message during activation, follow the steps in this article ☞ If you can’t turn on or sign in to iMessage or FaceTime - Apple Support