Googler, opinions are my own. I don't work anywhere near phone stuff.

I assume your friend has tried all the debugging on this page? https://support.google.com/messages/answer/9363493?hl=en My wife's phone keeps failing to connect and we have to do the carrier services reset to make it work. A terrible solution to me requiring factory resetting your phone.

But even then, I have a friend that was never able to get RCS to work on his phone, and he spent multiple hours with Google support trying to figure it out. There is something wrong with his account on Google and the carriers side (he tried multiple phones, and it never worked). The RCS team definitely has some corner cases to work out getting everyone activated, because it leads to really bad stories like this.