Add comment from primary source of this info:
but ONLY for 12XX, 13XX and 14XX Users:
To get this one working you MUST upgrade your GTM-25 Firmware to the very latest firmware, otherwise it won't work
After entering the code you need to reboot the unit and reattach the GTM-25. After that you can see all subscriptions in the traffic menu.
Note this only works with the GTM-25, NOT with GTM-12, nor with GTM-21.
P.S. Instead of 12XX, 13XX and 14XX you can read any devices that support TrafficProvider.xml. At that date the other units with GTM-25 has not yet been. All GTM-recievers greater then GTM-25 work fine also!