Revenues can only be settled to revenue-carrying senders (sales documents, billing elements, internal orders with revenues, profitability segments), or to G/L accounts.
Where revenue is not posted to a revenue-carrying sender (billing element, or order with revenues), the sender can also be settled to a cost center, business process, or asset. To be able to settle costs and revenues, you may need to create separate source structures for them.
Multi-level settlement is not possible in such cases, because the information that revenue has been posted is not transferred.
In your case the sender means order meight be in open condition or it meight be already closed(settle)
Please check once the order status.
If the purhage requisiton has been raised through order (components in order nonstock), then the cost will be settled against the order.
If you purchage the material as a stock item, then u can assign as a component in order.
In both cases no need to create settlement rule again. If once you release the order the settlement will be created automatically.
When you settle the order the additional costs will be settle against the order respectivey in KO88 after TECO.
First you see is there any Actual cost in order in cost tab page. Because settlement only donw ehen there is actual cost in order. Settlement not done on planned or estimated cost.
As you saying that material purchased from PR but is this PR generated from order. If yes then this error will not come.