I am trying to solve the same round trip problem mentioned in my other post below.
I created the same request with one driver but eliminated the route assignments and sequences. I added additional two order pairs . The two additional order pairs have the same geographic locations. The first order of each pair is a drop off while the second is a pickup. I did not specify and PickupQuantities or DeliveryQuantities on the stops so this should work. For some reason the out_stops response parameter returns back empty. All the stops go to out_unassigned_stops. To my surprise the violatedConstraint for all my stops is "MaxOrderCount exceeded" . Why is this the case ? I attached my request to this post for your reference.
Can you check the status messages for that solve? I believe it should be giving an error message about the orders in the order pairs being reused. An order can only be in one order pair so using the same orders for the order pair that connects the delivery to the pickup should be what is causing the problem.
I checked the status of the response as per your suggestion. I got a few warnings like the one below
Order Pairs (FirstOrderName = \"D-8057896\", SecondOrderName = \"P-8057898\") has a SecondOrderName value for an order that is already paired.
Looks like using order pairs is not an option for solving this problem. Unfortunately the api does not allow a stop to be used in more than one order pair.