If you're having issues, such as missing text messages (SMS/MMS), and you're using the same phone number from your previous phone, you may need to turn off RCS chats on your previous phone
With your previous device
Open Messages
Tap More options> Settings > RCS chats
Turn off RCS chats
Without your previous device
Google will verify the phone number is yours before turning off RCS chats. If the phone number you entered is registered with Google, you'll receive a 6-digit verification code.