Heated Bed doesn´t heat up

Hi, I've been working on my RatRig V-Core 3.1 for days and now I have the problem that the heated bed is not heating up. The temperature is displayed in RatOS and corresponds to room temperature. When I set 80 degrees, the red LED on the SSR lights up and there is 24V, but the bed does not heat up to the set temperature. The heated bed has a resistance of 48 ohms. What did I overlook? Regards