I'm assuming (I could well be incorrect as I'm new to Mercedes as a brand) that the Mercedes me services are free for the first three years and then you have to subscribe after that?
I only got my new car last November and according to my Mercedes me account online, all the services are showing as valid until November 2025.
Basically, the app connects every time if my phone is on wi-fi (either my home wi-fi or any wi-fi), but if it's on "data" (be that 3G/4G/5G), the app will not connect or update the stats. It was fine for the first couple of months of ownership but did seem to stop working when iOS 16.3.1 came along, but that might just be coincidence.