Unable to activate Messages on iPhone 6s at iOS 15.8.4

I've seen a lot of videos and a lot of resources that would be helpful but none of those work for me. A lot of them say to turn iMessage on and off and tings like that, but I'm unable to do that as it is greyed out on my phone. Im very ubnsure of what to do, can anyone help? If it makes any difference my phone is an iPhone 6s at iOS 15.8.4

[Edited by Moderator]

Original Title: How to fix waiting for activation