how to make barter loot table for custom mob

what im asking is basically when right clicked i want it to drop items from a loot table so i dont have to manually add the items one by one like this

https://imgur.com/a/pGuLDdx

another reason is that it will always drop the top item and refuses to drop any other item

basically im either asking for how to make them drop items in a loot table or how to fix this