Installed ATS PSU on MKS Gen 1.4, psu fan starts and stops (no replies)

So I have a corsair CX600 and I decided to install this on my 3d printer.

I am using a MKS GEN 1.4 with latest Marlin.

In marlin I set POWER_SUPPLY = 1

This enables the PS_ON_PIN on pin 4.

following various tutorials, I wired the green ATX wire to pin 4 using an adapter I made. Turned the PSU on and in OCTOPRINT I sent the M80 command. The fan on the PSU starts and then stops and it repeats this forever.
So I then disconnected my adapter and shorted out the green wire to black. Turned the PSU on and everything works fine

Any ideas?