Hi I have a aqua spa imperial inflatable hot tub , but when I turn it on the heater lights up and works but it don't heat up

You have posted twice about the same problem. Why don't you call the people you bought it from, or installed it?

It can't work and not heat up, I would clip and Amprobe around the Heater wire to check for draw, can check resistance of element if an Amprobe is not available.
I also say If it has power to the element and it isn't heating, the element is bad.