Put your pto selector in the mid pto only slot. The farthest to the front slot.
If that doesn’t rotate, slide the selector between the front selector slots and try to rotate the pto shaft.
WITH THE ENGINE OFF!!
My BB48x has been pretty tough. It is almost ten years old. It cuts really heavy brush one day. Then the next day it cuts heavy grass and it looks almost like a lawn.
I have had good service out of my little 48” brushbull.