My Heater only works when car is not moving

First thing is to check the coolant level. As the coolant leaks out and the level drops the heater will lose its ability to heat because the system doesn't have enough coolant. Let me know how this checks out. Another problem could be a faulty heater control valve, but lets take it one step at a time. It sounds like you have a temperature blend door actuator that is not working, bad engine thermostat or the engine is low on coolant, here is a video and guide to help you find the problem.

https://youtu.be/SNRb6pSwYuU

and

https://www.2carpros.com/articles/car-heater-not-working

Please run down these guides and report back.