Define the owner of every fact
For each exchanged field, decide which system creates it, which system may update it and what happens when information conflicts. Ambiguous ownership turns a useful integration into a recurring support problem.
Expect partial failure
External systems time out, change shape and send the same event twice. Design for idempotency, retryable work and visible reconciliation. A successful request from one API is not proof that the end-to-end business outcome happened.
Make change observable
Record versions, critical events and the smallest useful diagnostic context. That lets a team answer what changed without exposing private data in logs. Good observability protects both delivery speed and customer confidence.
