What is this 4 ?
It's the quick attach feature to lock front implements and/or mule drives in place.
You do NOT have the mule drive pushed in far enough to secure the latch in place!
Give it a good kick to lock it in place! That should be self evident I would think.
If it will not push further onto the large mount bolts on the d=side of the frame to engage the spring latch you must have the wrong mule drive for that application or something weird like that.