I recently switched to an iPhone 13 and the iOS version in Settings is 18.3.2. According to Wireless carrier support and features for iPhone in Asia-Pacific, my carrier is listed there too (in Vietnam). Previously I was using an Android and could send RCS just fine.
I have followed this guide Turn on RCS messaging on your iPhone but in the Settings, RCS Messaging
is not there.
Did I miss anything?
Update: when I use the Settings' Search feature, the option even shows up but when I tap it, it brings me to the Messages' app setting but there is still no such option.