If you are talking about the Bluedun app connecting then this stopped working in March for me. I contacting the app owner and sent him the diagnostics and it seems to be a timeout issue with Mercedes Online. It was never a great Mercedes system so no great loss but yet again Mercedes not giving...
As someone said earlier, within hours (if that) of the 20% offer it was pulled due to technical issues so is presently not available
interestingly the T&C page under service care shows the offer so contact the number and complain, it may shame them into fixing it!
The numbers can be influenced by atmospherics on the day as well as other factors so the important numbers are the before and after values and not just how big the number is as you could return with your car and get different values on another day