Follow a real order through every system
Begin with one realistic journey from product discovery and checkout through payment, inventory, order processing, fulfilment, delivery, and customer support. Mark which systems take part and which teams use the information at each point.
This exposes requirements that an API list can hide. A technical connection may be working while the business still has no clear answer for a cancelled order, delayed stock update, failed payment, or changed delivery state.
Define the source of truth for important data
Agree where product information, prices, inventory, customer details, and order status are mastered where those data types are relevant. If two systems can independently change the same value, the integration needs an explicit rule for which one wins or how conflicts are handled.
Also decide how quickly information needs to move. Real-time is not automatically better. The required timing should come from the customer and operational consequence of data being delayed.
Design for failure, retries, and duplicates
Network failures, third-party outages, invalid data, and temporary service limits are normal integration conditions. Define what happens when a message cannot be processed, whether it can be retried safely, and how the system avoids creating a duplicate order or repeating another business action.
A useful integration should make important failures visible to the people responsible for resolving them. Silent failure is often more damaging than a visible temporary interruption because the business can continue making decisions using incomplete information.
Keep a manual fallback for important exceptions
Automation should remove unnecessary manual work, but important business flows still need an exception path. Decide what staff can do if stock is wrong, an order cannot be exported, a payment needs review, or a fulfilment update does not return as expected.
The fallback should not become the everyday process, but it can prevent a technical exception from turning into a customer-service dead end.
Make ownership visible across teams and suppliers
An integration often sits between systems owned by different teams. Before launch, identify who can investigate each side, who can approve a change, and how evidence is shared when a problem crosses the boundary.
This matters particularly when the storefront, ERP, payment provider, fulfilment service, and infrastructure are supported by different organisations. Clear ownership reduces the time spent proving which system is responsible before anybody starts solving the customer problem.
Test timing, volume, and out-of-order events
An integration that works with one test order may behave differently when several events arrive together, a downstream service is slow, or updates arrive in a different order from the happy path. Testing should reflect the timing and volume patterns that matter to the business rather than only confirming that one API request receives a successful response.
For inventory and order flows, think about what happens when an older update arrives after a newer one, when the same event is delivered twice, or when one step succeeds and the next step fails. The right controls depend on the systems involved, but these scenarios should be deliberate design questions.
Move only the information the process needs
Integrations become harder to maintain when every available field is copied simply because it can be. Define the information required for the business flow and avoid creating unnecessary dependencies on data that nobody uses.
The same principle helps with privacy and security. Customer or operational data should not be sent to another system without a purpose. Limiting the payload reduces accidental exposure and makes mapping, validation, and future change easier to reason about.