Heat tape not heating?

I just got a t8 cage from AP. Got it all setup well when I hook the tape up to my hydro farm thermostat it will not heat the top of the cage up. Could this be because of the thermostat im using? Also I never used the heat tape before but I assume you can't use it wrong? Both sides heat correct? Any tips ideas welcome. Also the tape does get hot I can feel it on the bottom.

You may have issues getting flexwatt to make enough ambient heat in one of those cages...

Did you plug the flexwatt into the wall directly to see if it is working before plugging it into the thermostat?

I'm using a PVC cage as well and have my UTH set at 91.5 because its so thick. I also needed to use a heat lamp (100 watt) to get my ambient to 90 on the warm side.