I finally fixed the "Chat registration failed" error on my Galaxy! If your RCS chats aren't working, try this:
Wipe the gold contacts of the SIM card gently with a clean micro-fiber cloth.
The "Chat registration failed" error prevents you from using Rich Communication Services (RCS) in Samsung Messages. RCS allows for typing indicators, read receipts, and high-res media sharing over Wi-Fi or data. When registration fails, your phone defaults to basic, limited SMS text messaging.