dirtydaily

All I want to do is lock the door while the car is running. I saw that there is a service with the app but how do I know if my car is compatible with the app? If I can't do this I'm thinking about returning my car in the morning.. it's too old if I can't do something this simple. I don't care about paying a yearly membership... I just want to be able to lock my car while it's running.. I can do this on my 2007 Infiniti no problem.. this is a shame.

W205C43PFL

Depends, since you have a 2015, you need mbrace2 (mbrace for prior to 2016 models)
https://www.mbusa.com/en/mbrace2
Check with your dealership to see if they can aid you in purchasing the service. This service allows you to remote start your vehicle and will shut off the engine after 10 minutes.
Alternatively, you can unplug the physical key (the one you use to lock and unlock your glovebox) from your smart key and then lock all the doors with the button on the driver side (the driver door won't be locked with the electronic button inside the vehicle). Exit the vehicle and look for a spot where you can use your key, turn it in a direction (forgot which, sorry) until you see all doors are locked if not turn the other direction. If you turn once, it will lock and unlock the driver door only then if you turn again it will lock and unlock all doors, so turn as many times as you need.