iMessage not activated

Re:" iMessage not activated : My iMessage is not activated on iPhone 7 version 15.8.5"

Thank you for your post to the community,

and thank you for letting us know you have the most recent compatible iOS version for your iPhone.

Apple support have an article online (link below) providing trouble-shooting steps to follow:

See what to do: If you can’t turn on or sign in to iMessage or FaceTime on your iPhone - Apple Support

If needed:

Apple's Support website: Messages for iPhone, iPad, Apple Watch, and Mac - Official Apple Support