How to record the process of orders at a fulfillment center?

We produce our own products. They are produced in-house then shipped to a fulfillment service.

I am not sure if our process/system is correct. Can you please let me know? 

1) When we send inventory to the fulfillment center, we create a zero-cost bill - for example, we send a quantity of 50 of SKU 123. In the bill we show a -50 of SKU 123 and a +50 of SKU Y-123 (we use the Y- as an indicator that the item is located at the fulfillment center). Question: should we include the cost of the item in the -50 and the +50?

2) When there is an order from our online store, we create an invoice in our system for the Y- item at fulfillment.

3) We create a PO to Fulfillment for the Y- item. The cost is zero for the item on the PO.

4) When Fulfillment ships the order, they create a zero-cost invoice  (except shipping) which we receive as a bill to us.

5) We pay the bill when it's due.

We have Quickbooks Online Plus.