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 chat features off on your previous phone
With your previous device
Open Messages
Tap More options> Settings > Chat features
Turn Enable chat features off
Without your previous device
Google will verify the phone number is yours before turning chat features off. If the entered phone number is registered with Google, you will receive a 6-digit verification code.