1) The car key is turned off and your particular car might require the key to be turned on to 'accessory mode' or the car may need to be running to provide power to the socket. Some auto manufacturers allow the socket to be powered with the key off or even out of the car and some need the key to be switched on.
2) Plug in another device like a phone charger to see if it lights up or powers up your device. If it does not, and the car key is on, then you may have a blown fuse. Consult your owners manual to find the fuse box and the specific fuse to the accessory socket and inspect it to see if it is broken. The heater draws 9 amps and most car accessory port fuses are 10 amp fuses, so the heater is designed to not blow the fuse. If it is broken, then replace it. If the new fuse does not fix the problem, then you may have a loose or damaged wire. Time to see a mechanic!
3) The heater got damaged in shipping. If this is the case, please try the heater in another vehicle that you know has a working accessory socket. If it still doesn’t work, please contact us and we will replace your heater with a new one if it is still within the year.