How are returns of items made in POS

I sell yarn in a small lokal yarn shop.

My clients knit sweaters and bring back their remaining skeins when project is finished and I give them back the money.

In my old pos, this was done with a button for returns (Retoure) and negative quantities. The accounting was made directly against cash or the corresponding payment method. This is, strictly speaking, mandatory for Germany.

I don’t know how to make these returns in the POS of erpnext (V13).
Negative quantities/payments are not allowed. If I try to make a Return (Credit Note) using the form view, I cannot make the POS Closing Entry because the POS invoice with the sold items is already closed.

I do the POS Closing Entry every day and I can not know if and when customers will bring back the items.

For me, the best solution would be to allow negative quantities because customers often take other items with them. Then the negative quantities are on the printed receipt and the remaining amount paid also appears.

At the moment I take the difference from calculator and create a Delivery Note for the returned quantities so that the stock inventory is correct again but the Revenue is not correct.

How should I do these returns the right way in POS of erpnext V13?

After update to ERPNext: v13.7.0 (version-13) the return of items works properly.
I added return_against and is_return to pos-settings.

The only thing I would love to see is the possibility to add additional items to POS Invoice.
For now I added a new mode-of-payment for the returns. So the customers are able to see the amount of returned items.