Open your Messages app
Tap your profile icon or the three-dot menu
Go to Messages settings
Tap Chat features, RCS chats, or Advanced settings
Turn off Chat features or RCS chats
If prompted, confirm that you want to disable RCS
Send a new message as a regular text message
If needed, restart your phone
If needed, turn off Wi-Fi and mobile data for the message to send as SMS
If you are switching phones, unregister your number from RCS before using SMS only