Go to the location shown below and add the pin shown in the image below to the ClientOpenExtInv event.
Add the highlighted nodes shown in the image below, location at the top of the image.
Go to the location shown below and add the pin shown in the called InventorySlots and set it to S_InvSlot and set it to an array. Then copy the image below. If you get the note on the node you can ignore it as it is an engine bug.