ForceTermination gives internal server error about ps.fritzbox.api HOT 4 CLOSED

namespace PS.FritzBox.API
{
    /// <summary>
    /// class for getting informations about the wan ppp connection
    /// </summary>
    public class WANIPConnectionClient1 : FritzTR64Client
    {
        public WANIPConnectionClient1(string url, int timeout) : base(url, timeout)
        {
        }

        /// <summary>
        /// Sets the control url
        /// </summary>
        protected override string ControlUrl => "/igdupnp/control/WANIPConn1"; //igdconnSCPD.xml

        /// <summary>
        /// Sets the request namespace
        /// </summary>                                 
        protected override string RequestNameSpace => "urn:schemas-upnp-org:service:WANIPConnection:1";

        /// <summary>
        /// Method to force the termination of the ppp connection
        /// </summary>
        public void ForceTermination()
        {
            try
            {
                this.Invoke("ForceTermination", null);
            }
            catch (Exception)
            {

                ;
            }
        }

        /// <summary>
        /// Method to request the termination of the ppp connection
        /// </summary>
        public void RequestTermination()
        {
            try
            {
                this.Invoke("RequestTermination", null);
            }
            catch (Exception)
            {

                ;
            }
        }
        /// <summary>
        /// Method to request a ppp connection
        /// </summary>
        public async void RequestConnection()
        {
            XDocument document = await this.Invoke("RequestConnection", null);
        }
    }
}