Yes, this is this value you will use. You set an int with the same value in item blueprint and when you add it to inventory :
if you haven’t set your widgets in an array : you do a “get all widgets of class” with inventory slot widget class selected. From “found widgets” you do a for each loop with break. From “array element”, you get your “inventory slot number”, you check that it is = dragged from item “inventory slot number” / branch : true : set item in slot and link to break to exit loop.
If you have an array, you simply “get” your slot from array, using the value as index (assuming you have arrange widgets in the right order when you create array, for example on event construct make array with all widgets added in right order (yes boring, why doing a procedural can be cool : you do loop : create widget, set index with loop index set it in uniform grid (using row and column) and add it to array) then you set item in this slot as before. Big advantage is that you avoid the loop which can be huge as you have 120 slots.
both will work the same with a stack, you just have to add another int for quantity.
If some items have no particular slot, you’d better separate if you loop but if you have an array, you just set a “free” value like last value + 1 and do a branch before loop, if value = free value, then you set item in free inventory, if not then you get value from array.