Full Body IK Mannequin Example?

I’m trying to make sense of the FBIK solver, just to make the limbs stick together when I move a bone, but I cannot make sense of it, has anyone ever managed to get it working for the mannequin (and i mean full body ik, not just partial ik using the full body solver)

■■■■ thing is documented about as well as the engine itself (as in practically not documented at all) so I feel like i’m fumbling in the dark a lot without any guidance and it really just isn’t working out.

I mean look at this, all i’m doing is creating the node and adding those few bones to it:

And so I set pin rotation to 0 which fixed that, then i add another bone, the thigh, and everything goes 10x more to hell for no discernable reason

So I undo that and check with the way it was before (but with pin rotation on 0) and move the foot.

Only to find that the fbik isn’t doing anything at all in the first place.

How is this even supposed to be done?