In that case, clear BOTH Cache & Data for Google Messages & Reboot.
You'll have to Enable RCS (chat) again.
It's also possible that the SIM card may need to be replaced?
You can check by using the Diagnostics on Samsung Members app & run the Diagnostics for the SIM. See if you get any error messages?
Hi, as you have tried using Google messages app to enable RCS feature, but still it is not working, we recommend you to please check with your service provider if they support on your device and to enable it.