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Conflict Handling

Conflicts can occur when the POS and the external OMS act on the same customer order simultaneously. For example, a store associate may be handing out an order to a customer at the same time the external OMS is cancelling that order. This scenario applies to both the Proxy and Events integration approaches.

How Conflicts Are Handled​

Events Approach​

When using the events approach, the Customer Order service handles conflicts automatically:

  • The service ensures the most up-to-date information is processed, and resolves conflicts in a way that keeps the order consistent.
  • 🛑 Pickup takes precedence over cancellation. Once the POS has handed an order to the customer, that order is closed to further change. A cancellation arriving afterwards is refused — the goods have gone, and no message can undo that.

How you find out. The refusal comes back on the request itself, so check the response rather than assuming acceptance.

You will also already have known: the pickup was published to you on the order updates stream when it happened, before you sent the cancellation. What the refusal does not produce is a second, separate notification — so do not wait for one.

⚠ The same rule applies to any closed order or fulfillment, not only to cancellation after pickup: once something is fulfilled or cancelled, it is final.

Proxy Approach​

When using the proxy approach, the external OMS is responsible for implementing conflict resolution logic on its own side. The external OMS must:

  • Monitor PosLog events to detect when orders have been picked up or otherwise updated at the POS.
  • Implement logic to prevent conflicting operations (e.g., cancelling an order that has already been picked up).
  • Ensure data consistency between its own system and the POS by reacting to PosLog events in a timely manner.