Android users: Make sure that your GPS is turned on at all times. If you only turn it on when going to the movies, it will take some time to warm up.
iPhone users: Under "Privacy" in your phone's settings, make sure that your location services are turned on for the phone in general and then specifically for MoviePass.
Always, select "Yes" or "OK" if the app asks you to allow MoviePass to access your location.
If you are still having issues, call 877-646-2892 when you arrive at the theater.