Ah, I see.
The shaft has a slot in the end that fits into the drive shaft to the oil pump.
It will only engage into the slot in 2 positions.
The camshaft drives the pump which has several teeth, so it has several positions that those two parts can engage.
You can gently push down while turning the motor over to get the oil pump to engage.
You can also lift the pump out and attempt to pre align the slot at the end of the shaft to get it close.
The gear causes the shaft to turn slightly as it meshes with the camshaft gear teeth.
You'll feel it when it drops in all the way.