For a return supplier from WMS warehouse it is not possible to work with a purchase type that immediately creates a receipt.
Within WMS this means that a booking must be made at a location (just as well as with a counter sales order). That is the difference with the situation without WMS. There is no provision for this within the WMS. There are then two options:
1. You create a separate purchase type, where a receipt is not created immediately. That may only be negative. You can then create a purchase order with this purchase type. You will then have to do the goods receipt separately with this negative number.
You can specify the location with the receipt booking. Note that this must be a release location. We assume that the goods are at a location. Via a location relocation, this can then be canceled against the negative number at the unloading location.
2. Or create a negative purchase order with purchase type whereby a receipt is created directly at another (fictitious) warehouse without locations. Then with a warehouse transfer you can transfer the goods from the location warehouse to the other warehouse of the return purchase.