How to add a product only to a (single) supermarket

[Nisbo]

Maybe I dont understand how it works.
I created

• some supermarkets
• some categories like food, drinks ..

I assigned the categories to the supermarkets, every supermarket has the same categories.

If I try to add something to the shopping list, I click on the supermarket name on the top and add milk to the chart, but its added to all supermarkets with the "milk category". Sometimes there are special offers and I want to by the milk in supermarket A but the milk is also shown in B and C. (B and C have also the food category)