Go to the BP_MasterInventory and create a new function called DestroyContainingInventories then copy the image below. You wont have the DestroyItemInventory function yet, go to the next step to create it and then come back to the DestroyContainingInventories function and add it in.

Next go to the BP_GlobalInventoryManager and create a new function called DestroyItemInventory then copy the image below.

Go to the BP_MasterItemSpawner and add the highlighted nodes shown below, location at the top of the screenshot.