In order to make sure that you can use iMessage with your eSIM plan you must:
- Make sure that the plan is enabled. Go to Settings/Mobile Data and ensure that the eSIM plan is set to ON.
- Make sure that you have a good signal for the eSIM plan. The iPhone sends and SMS to a specific number in order to retrieve the phone number ( MSISDN ) for the eSIM plan.
- Toggle the iMessage setting OFF and ON. Go into Settings/Messages and turn iMessage OFF. Then turn it ON again.
- In the same Settings page click ‘Send & Receive’ and ensure that the eSIM plan is ticked as an address that you ‘can receive messages to and reply from’.