Studio Session Handover to Cognigy failing with 401

How do I pass the session token correctly? I’m using GetRESTProxy in Studio to post to the Cognigy API. The endpoint works in Postman but fails in the script with a 401 error. The payload looks right. Here’s the JSON I’m sending:

{"sessionId": "123", "token": "abc"}

Is the token expiring too fast or is the header wrong? The docs are vague on the auth flow for handovers.