Outbound Campaign API 409 Conflict during Zendesk Migration

I’m trying to figure out why the /api/v2/outbound/campaigns endpoint returns a 409 Conflict error when importing our Zendesk outbound list. The JSON payload matches the schema, yet Genesys Cloud rejects the creation with a duplicate key violation. What is the correct way to handle unique ID mapping for outbound contacts during a Zendesk-to-GC migration?