Use case:

Some regular customers mostly buy large amounts of products directly from the general office (using the sales app), but sometimes they are in a rush and go to one of the shops that are near them (the shop uses PoS).

The customer takes the products from the shop but, as they are regulars and the owner thrust them, they do not pay there. Instead, they wait a couple of days or a week and then they go to the general office to pay directly to the owner.

To sum up, the customer takes products out of the shop's inventory but he pays at the general office. So, inventory is out of PoS but has no payment.