Sipsorcery Auth for Scaip/XML

Question

I'm sending scaip xml messages. With a server which doesnt have a password everything works fine. Now in the next step one server requires a password autentication.

When I look at this documentation I expect a response which challenges me to create the psaswort with which I would need to reply. But I don't get any response. Do I need to bind somewhere else ? Am I missing? Is my expectation correct that a response should be received for the auth?

Simplified Code:

    using var sipTransport = new SIPTransport();
    sipTransport.SIPTransportRequestReceived += (a,b,c) =>
    {
        Console.WriteLine("Request received");
        return Task.CompletedTask;
    };
        
    sipTransport.SIPTransportResponseReceived += (a,b,c) =>
    {
        Console.WriteLine("Response received");
        return Task.CompletedTask;
    };

    var uriFrom = new SIPURI(fromUser, localIp, null, SIPSchemesEnum.sip, SIPProtocolsEnum.udp);
    var uriTo =  new SIPURI(toUse, context.ProviderConfiguration.GetString("host"), null, SIPSchemesEnum.sip, SIPProtocolsEnum.udp);

   var sipRequest = SIPRequest.GetRequest(SIPMethodsEnum.MESSAGE, uriTo,
        new SIPToHeader(
            null,
            uriTo,
            null),
        uriFromHeader);

    sipRequest.Header.Contact = new List<SIPContactHeader>()
    {
        SIPContactHeader.GetDefaultSIPContactHeader(SIPSchemesEnum.sip)
    };

    sipRequest.Header.ContentType = "application/scaip+xml";
    sipRequest.Body = body;
    var callResult = await sipTransport.SendRequestAsync(sipRequest);