Outbound Campaign API 400 on Zendesk List Import

So I’m seeing a very odd bug with the Outbound Campaign setup. Trying to import a Zendesk ticket-based contact list into Genesys Cloud via the API. The mapping looks correct, but the endpoint rejects the payload.

POST /api/v2/outbound/campaigns
Status: 400 Bad Request
Error: Invalid contact list reference

The Zendesk list ID is being passed, but GC expects a native list UUID. How do I bridge this gap during migration?