Where it usually breaks
And how to keep it from happening.
- Unresolved stock authority. Product presence in the catalog does not establish the right to allocate another system's stock.
- Repeated event. A repeated shipping message must not create an additional physical handover quantity.
- Mixed stages. Adding allocation and shipping quantities together overstates the units being fulfilled.
- Return mistaken for refund. Keep the physical event and verified provider refund distinct in the customer discussion.