Where is the grounding port in the RB750UP?

Hi guys,
I’ve a RB750UP and I’ve some outdoor units connected to it, in Ubiquiti ToughSwitch I can ground the unit easily, but I don’t know where to ground the RB750UP.

I’m attaching an image here…

Ground it through the PSU power cable, it contains a third wire for grounding, you will not need to open the router case.