A negative stock for an item can occur due to an overlap of orders with different payment methods (one of them prepayment). However, since orders with the payment method prepayment are now also reserved in our system for 7 days and usually also paid in this period, it is now rare to overlap.
If this does happen, please set the item status of the last order received to "Händlerstorno" (vendor cancellation) so that customers are informed immediately by an automatic email.
The stock will be automatically set to 0.
Then write to our customer service, they will correct the cancellation in your favor, so that no commission is incurred for you.