Set to agents direct queue dynamically

Hello,

I am attempting to dynamically select a customers account manager to take incoming calls for certain accounts. I have been following the instructions here: https://docs.aws.amazon.com/connect/latest/userguide/contactflow.html#transfer-to-agent

I created a lambda function to return the agent Id

        var resultMap2 = {  
            agentID:agentid,  
        };  
          
        callback(null, resultMap2);  

This is working perfectly, and it is returning the ID to my contact flow just fine. When I go to set the working queue (by agent > use attribute > type:external attribute:agentID) It errors out.

I'm just wondering if anyone sees any glaring issues here? Or if anyone has been able to set this up? I have tried to use other agent fields like username and ARN but neither are working.