Unique metadata shop items

I’m using ox_inventory shops.
How can i add a custom metadata (unique for every item like licence number or weapon serial) to an item selled by NPC shop?

All you need to know is on Metadata - Ox Inventory

could be, but i’m not understanding.
i don’t want that every time someone buy an item from the shop, all item selled have same metadata.
what i want is every item purchased even by same player, has a metadata with unique id.
can you please help me with example code?