OnShape - Laser Joint & T-slot Joint Featurescripts

Can't seem to apply tab and slot joint between the two Base-flanges I don't understand what the problem is

Locked Tab and Slot Joint Locked tab and slot joints are good to use in various utility projects and in toy making when building and

tab slot Holes or slots in the arrow side member of a joint for plug or slot welding must be indicated by placing the weld symbol on the side of the

tab and slot weld I did the tab and slot joinery and used 12 Birch ply for my holders I sized everything based on the number of tabs and slots