Apple is doing insane stuff with iMessage making SMS useless with Android. It is intentional manipulation. I’ve only seen it on some Apple kernels with the latest iPhone. My old man’s phone absolutely will not send or receive an SMS unless I message is manually turned off and then it won’t get iMessages. Apple has always been a shitty company, but this is next level insane. Just get and use the Signal app and ditch all the proprietary garbage and manipulative bs IMO.

Haven’t used RCS since Google intentionally caused it to silently fail on rooted devices

So I’m not sure if this is the problem affecting your friend, however, RCS messaging uses additional ports rather than just the standard tcp/443 port to send traffic. This port is specifically tcp/5223. If your friend connects to a wireless network that has a firewall that doesn’t have the port open, then the RCS messages will fail to send/receive until they are either connected to their cellular network or a wireless network that doesn’t have that port blocked.

The catch is, if you try to send a message while you are on a network where the traffic isn’t allowed, the RCS message doesn’t attempt to resend right away after changing to a network where the traffic is allowed.

I have a firewall in my house that has very strict rules and I had to enable a firewall policy to allow this traffic to be able to send / receive RCS messages when I was connected to my home’s WiFi. My wife’s company WIFi network has that port blocked so she doesn’t connect to it anymore and RCS works just fine.

If you want to see if this is the case for your friend’s phone, have them use their mobile network while sending / receiving RCS messages to test.

Working fine for me so far but a lot of people I know haven’t upgraded their iPhones so our messaging hasn’t switched to RCS. But the few conversations that have switched are working fine.