I upgraded from a Note 8 to a Note 10+.
RCS worked on my note 8 but not on the Note10+. Samsung says it's a service provider setting or an initialisation they needto send to my handset, Neither Boost or Telstra seem to know what I'm even on about.
Are you using the Google Messages app?
If so, in the app, go to Settings > General > Chat Features and then check the status there. If it is stuck in status "pending", you may have to hit "retry" and follow the prompts.
Not sure if the process is different on other message apps.
* I am a Boost Australia customer. This is a peer to peer community where users help each other.
I'm using the standard Samsung messages. ( No Chatt settings option)
I downloaded Google messages and the Chatt features says it is unavailable for this device. Your device does not currently support this feature. "Learn more" (link broken)