The best integration plan is not a list of APIs. It is a shared description of what should happen, which system is responsible, how quickly data should move and what the team does when it does not.
Begin with the operational result
Write the target workflow in plain language before discussing endpoints or middleware. For example: a completed store sale should reduce the correct stock pool, record the matching payment, update the customer profile when consent exists and reach finance with the references needed for reconciliation.
This creates a common testable outcome for operations, finance, ecommerce and technology teams.
Choose one source of truth for every key record
Decide where products, prices, inventory, customers, orders and payment references are mastered. When two systems can edit the same record without a clear rule, integrations tend to amplify inconsistency.
For each data object, document the system of record, permitted editors, update direction, expected delay and recovery method.
Map the events that cross system boundaries
Cover routine and edge-case events: sale completed, refund issued, order cancelled, stock received, item transferred, customer merged, payment reversed and settlement received. Give each event a durable identifier so teams can trace it across connected platforms.
- Define which event starts the workflow.
- Carry the original order and payment references.
- Make retries safe so the same event is not posted twice.
- Record status changes for support and audit.
Design the recovery path before launch
Connectivity will fail, credentials will expire and data will occasionally arrive in an unexpected form. A production-ready design queues recoverable events, isolates invalid records and alerts the right owner with enough context to act.
For a multi-outlet retailer, the fallback should also explain whether stores may continue trading offline and how queued transactions are reconciled later.
Test business scenarios, not only connections
Technical connectivity proves that systems can talk. Acceptance testing proves that the complete workflow works. Build test cases around real trading scenarios and confirm the result in every downstream system.
- Complete and refund a normal sale.
- Use multiple tenders and partial payment where supported.
- Transfer and return stock across locations.
- Apply loyalty earning and redemption rules.
- Reconcile orders, payments and settlements.
The final checklist should name the owner of each test and the evidence required for sign-off.