CXone Studio Session Handover to Cognigy failing with 500 Internal Server Error

We’re trying to set up a voicebot handover in CXone Studio for our Central time zone support queue. The goal is to let the NICE Cognigy bot handle initial intent classification before routing to a live agent if needed.

I have the Studio flow set up with a “Transfer” action. The target is a “Session” type, pointing to our Cognigy endpoint. Here is the JSON configuration I’m using for the transfer:

{
 "transferType": "SESSION",
 "sessionEndpoint": "https://cognigy-api.nice.com/v1/...",
 "parameters": {
 "conversationId": "{{Conversation.Id}}",
 "agentEmail": "{{Agent.Email}}"
 }
}

When the call hits this node, it immediately fails. The Studio logs show a 500 Internal Server Error. The error message isn’t very helpful, just says “Failed to establish session”.

I’ve double-checked the endpoint URL and it looks correct. I’m passing the auth token in the header via a previous Assign node, but I’m not sure if the Transfer action supports custom headers out of the box.

Has anyone got a working example of passing the Bearer token correctly to Cognigy from Studio? Or is this a known limitation with the Session transfer type?