Choose a matching authority
Decide which system owns contact identity and which stable ID the connector stores. Keep the provider account and business line with the mapping; the same recipient may legitimately contact two businesses or departments. Normalize phone data with the supported tooling in your stack before comparing it.
A phone number is a useful lookup value, but it should not be treated as proof that every matching record represents the same person or relationship.
Write the exception path
When more than one eligible record matches, send the case to a review queue with enough context for an administrator. Preserve the original message reference and avoid launching two follow-up sequences while someone resolves it.
If records are merged, define how the messaging mapping changes and which history remains visible. Check this with a test contact before relying on a bulk CRM cleanup.
Use a small repeatable fixture
Create two synthetic records sharing a test number, send a consented reply and inspect the resulting association. Repeat after a merge and after changing the assigned representative.
Pass the integration only when the team can explain each result and recover from a wrong association. Keep the fixture and the expected behavior with the connector’s operating notes so a future update can be checked.