RTCPeerConnection.CreateAnswer() fails

Question

I am trying to set up the signaling between a browser client and unity client. the two clients use Webrtc and I am using a websocket to make the signaling happen. First, I am creating an offer on the click of a button in the browser. the offer reaches the c# client and the localConnection.setRemoteDescription works fine, then I need to create an answer. Instead the answer is an empty object recieved

{"type":0,"sdp":null}

Any Ideas if there is something wrong?

 public void handleIncommingMessages(object sender, MessageEventArgs e) {
        
        SignalingMessage message = JsonConvert.DeserializeObject<SignalingMessage>(e.Data);
        
        switch (message.type){
            case "offer": handleOffer(message); break;
            case "answer": handleAnswer(message);break;
            case "ice-candidate": handleIceCandidateMessage(message);break;
        }
    }

void handleOffer(SignalingMessage offerMessage)
    {
        localConnection.SetRemoteDescription(ref offerMessage.sessionDescription);
     
        RTCSessionDescriptionAsyncOperation answer = localConnection.CreateAnswer();

        Debug.Log(answer.Desc.sdp);
        SignalingMessage answerMessage = new SignalingMessage {type = "answer" , sessionDescription = answer.Desc , iceCandidate = null};
        socket.Send(JsonConvert.SerializeObject(answerMessage));
    }

this is the implementation of the SignalingMessage class which represents any message to be sent over the websocket

public class SignalingMessage
{
    public string type;
    public RTCSessionDescription sessionDescription;
    public RTCIceCandidate iceCandidate;

}