Decide who owns each fact
Before writing an API, agree where each record begins and which system may change it. Product descriptions might come from a PIM, customer terms from ERP and browsing behavior from commerce. Document what should happen when an update arrives late or conflicts with an existing value. A single vague promise to “sync everything” cannot answer those questions.
Treat flows separately
Catalog publication and order submission have different urgency and failure costs. Some data can move in scheduled batches; an accepted order may need immediate confirmation and durable retry behavior. Design each flow around its business consequence. Keep identifiers and mappings visible, and make transformations testable rather than burying them in many unrelated endpoints.
Design failure as part of the journey
Networks time out, fields are missing and upstream systems become unavailable. Decide whether a failed step should be retried, held for review or rejected with a clear reason. Operators need to know which business object is affected and whether it is safe to run the step again. That is more valuable than an integration that appears seamless only when every service is healthy.
Watch the business flow
Monitoring should answer operational questions: which orders have not reached ERP, which catalog updates are stale and which customers cannot see their correct prices? Technical logs help diagnose failures, but a business-level view helps teams act. Start with the few flows that determine customer experience, then extend the integration without losing ownership and visibility.