Error code 502 means the device doesn't recognize the vehicle's stock information as a supported application.
Please double-check that the vehicle you are attempting to install on is supported by your device. You can search for supported vehicles here.
If you are receiving this error and the device you own does support your vehicle, you may need to update the GT. To install the Update Agent click here.
If you continue to have this issue, please get in touch with us at techsupport@derivesystems.com or visit our chat option on our site, bullydog.com. Make sure you have access to a windows based pc, the device, and the vehicle when you do. Thanks.