Mine frequently won't connect to my car. Try the following (If you haven't already) in order !
1. Sit in the car and go into the infotainment screen and go to Settings and on the right side scroll down to Privacy Policy - Make sure everything is Agreed and turned on.
2. While stilll in the car go to the User icon on your infotainment screen (swipe right = see attached Youtube video) and make sure you are logged in. If not login.
3. Make sure you are parked outside away from high buildings, unlock the car and lock it again 30 seconds later and check the app.
4. Unlock the car, sit in it and go to the charging tab as if you were about to charge. Open the charging door and check your app again, especially the Charging Management menu in the top left three = line menu list.
5. When you are out next in the car, try driving to a location with excellent mobile reception and try 3 and 4 above again.
6. If all falis keep trying each day as the MG servers can be hit and miss.
7. After a week, if it's still not working I would contact your dealer as perhaps it's not been registered properly on the MG Server or your cars e-sim is not working ?