By default, for orders imported in the status [1] Incomplete Data (which is initially the case for prepayment orders), no stock is reserved. However, you can change this in the order settings to reserve stock starting from this status.

Step-by-step guide to stock reservation

1. Open the menu Setup » Orders » Settings.
2. Find the setting Order reservation status (reservation of stock).
3. Select the status [1] Incomplete Data in the dropdown list for the option from.
4. Select the option All orders in the last dropdown list.