TL;DR

• Users who have rooted their phone, have their bootloader unlocked or are using some custom ROMs report that their RCS messages are not being sent, even though RCS shows them as connected.
• The Google Messages app does not show any error messages when blocking RCS messages of these users and does not send the messages out as SMS or MMS either.
• Google famously campaigned for Apple to include RCS messaging in iMessage but is now blocking it for certain Android users.