Why can’t I send or receive text messages from my iPhone 12 Pro max
My service is on
My service is on
iMessage (Blue) -

SMS/MMS (Green) -

It will turn from Blue to Green if you have enabled "Send as SMS" and whenever your iPhone is not connected to the internet it is sent as SMS (green) to all iPhone users.
You need to have an SMS/MMS plan enabled by your carrier for the SIM/eSIM that you use on your device. Apple Inc does not provide SMS/MMS services.
Why can’t I send or receive text messages from my iPhone 12 Pro max