Hi, 

we are building a site where everthing is basically free, meaning cost = 0 of all variants. We can do the purchase order in code of course, but it seems there is some hard checks in commerce manager where it is impossible to release a shipment if there is no payments associated with a purchase order.

When creating a purchase order with line items not having any cost it is impossible to add payments to the order from commerce manager. Which makes a lot of sense as there is no cost associated with the order.

The code blocking the release of the order is in:

 Mediachase.Commerce.Manager.Order.CommandHandlers.PurchaseOrderHandlers.ReleaseShipmentHandler

right here:
if (purchaseOrder.OrderForms.Count == 0 || purchaseOrder.OrderForms[0].Payments.Count == 0 || purchaseOrder.OrderForms[0].Shipments.Count == 0 || (purchaseOrder.OrderForms[0].CapturedPaymentTotal + purchaseOrder.OrderForms[0].AuthorizedPaymentTotal) < purchaseOrder.OrderForms[0].Total)
{
CommandHandlerHelper.ShowInfoMessage(OrderStrings.Order_PurchaseOrder_PaymentLess, base.CommandManager);
return;
}

Notice that it is checking for Payments on the order and if there is none it will refuse to release the shipments.

How would I go about creating such an order from commerce manager? It will be customer care people doing this and not developers of course.

I can see two possible ways of fixing this: 
1) Telling customer care to add a dummy cost to one of the items so they can add a payment and then release the order

2) Creating a custom implementation if the ReleaseShipmentHandler and configuring it in the commerce manager, this will of course be destroyed the next time we update commerce manager from NuGet.

Any other suggestions?