Buy Button Transaction Error: "this item is no longer available"

Dear @marentsen ,
I think the error message comes from using “user specific columns” and/or “row owners”, as discussed here and here.
For your case: I think it is best to work with a “orders” sheet, let users configure new orders, add a row for every new order, use the orderID in the buy button’s SKU/ProductID, and add a buy button to place a new order. Then you can make relations in glide to the “App: Sales” sheet once copied to a new sheet in gsheets or use lookup in gsheets without copying the sales sheet.