I have no idea if the DMS is original or not. Im gonna take a wild guess and say no. If its not original, will it work in a original keg?
If the DMS is not original, it will not work in your keg, since your keg has not been hacked to work with non-original disks.
Let's assume for now that it is an original (and if it's not, you should get your money back), and the reason it's not working is because it was used with a different head unit. Use the Phathack DMS Tools in Tools mode to update the firmware on the DMS to whatever head unit you have. Tick the boxes to "install non-hacked firmware" and "reflash box with firmware."
Once that's done, take the DMS out to the car, and with the car radio turned OFF, insert the DMS into your box/keg. Turn on the radio, and the box should power on. The green light should be blinking. Once that starts, you can shut everything off. Give it 10 minutes, more or less, and then it should stop.
When it's finished, take the DMS back inside, load some music on it, and then back to the car to test. You may have to disconnect and reconnect the box to initialize the connection between it and your radio. If everything has gone right, it should work.