RCS chat on Messages not working

One of my friends also have an Android phone, and ever since we've been texting, we've been using the RCS chat. Recently, I went outside the country, and the chat defaulted to SMS instead. Fine. But since I came back, when my friend texts me, it shows that the message is an RCS message, but I am only offered an SMS in reply. I tried all the options I could figure out. I cleared the cache, restarted, in airplane mode and not, both for the Messages and Carrier Services. I've disabled chat-restart-enabled chat. Nothing works. Does anyone have any idea what I can do, other than stop texting with my friend? If it matters, I'm using a Pixel 3XL with up to date Android.