List Shifter: Reverse, Rotate, Swap and ITERATE (Loop) Over Bubble Lists | Now Part of Floppy

Sounds like all you’re doing is building a shopping cart, really. In your case, a line item in an order has not just the item in question and a price, but an additional bit of data indicating who the item is for.

While I don’t address your specific use case, it might be useful to watch this video about shopping carts. In it, I do show how you might construct and process an order on the backend (using server side plugin List POPPER) to iterate over line items: