All world actors are located under Game/EconomyKit/Blueprints/WorldActors. You can setup items in Game/EconomyKit/Blueprints/Data/ItemData.
Drag a BP_MoneyLoot in your scene and on the right of the details panel select the amount you wish to use for said coin stack.
Drag a BP_Vendor in the world, and on the right you see a details panel with “Items To Sell”. These have to be the items you setup in the datatable in Game/EconomyKit/Blueprints/Data/ItemData with the exact row name(Caps sensitive).
The kit will list said items in the order you list them, so if you list a weapons item first, the weapons category will be first too.
Drag a BP_LootItem in the world and set the ItemID and amount on the right details panel. The amount will be capped to the item’s max stack.