/// <summary>
        /// Retrieve a list of available phone numbers that can be purchased and used for your Ytel account.
        /// </summary>
        /// <param name="numbertype">Required parameter: Number type either SMS,Voice or all</param>
        /// <param name="areacode">Required parameter: Specifies the area code for the returned list of available numbers. Only available for North American numbers.</param>
        /// <param name="pagesize">Optional parameter: The count of objects to return.</param>
        /// <return>Returns the string response from the API call</return>
        public string CreateAvailableNumbers(Models.NumbertypeEnum numbertype, string areacode, int?pagesize = null)
        {
            Task <string> t = CreateAvailableNumbersAsync(numbertype, areacode, pagesize);

            APIHelper.RunTaskSynchronously(t);
            return(t.Result);
        }
        /// <summary>
        /// Retrieve a list of available phone numbers that can be purchased and used for your Ytel account.
        /// </summary>
        /// <param name="numbertype">Required parameter: Number type either SMS,Voice or all</param>
        /// <param name="areacode">Required parameter: Specifies the area code for the returned list of available numbers. Only available for North American numbers.</param>
        /// <param name="pagesize">Optional parameter: The count of objects to return.</param>
        /// <return>Returns the string response from the API call</return>
        public async Task <string> CreateAvailableNumbersAsync(Models.NumbertypeEnum numbertype, string areacode, int?pagesize = null)
        {
            //the base uri for api requests
            string _baseUri = Configuration.BaseUri;

            //prepare query string for API call
            StringBuilder _queryBuilder = new StringBuilder(_baseUri);

            _queryBuilder.Append("/incomingphone/availablenumber.json");


            //validate and preprocess url
            string _queryUrl = APIHelper.CleanUrl(_queryBuilder);

            //append request with appropriate headers and parameters
            var _headers = new Dictionary <string, string>()
            {
                { "user-agent", "APIMATIC 2.0" }
            };

            //append form/field parameters
            var _fields = new List <KeyValuePair <string, Object> >()
            {
                new KeyValuePair <string, object>("numbertype", Models.NumbertypeEnumHelper.ToValue(numbertype)),
                new KeyValuePair <string, object>("areacode", areacode),
                new KeyValuePair <string, object>("pagesize", pagesize)
            };

            //remove null parameters
            _fields = _fields.Where(kvp => kvp.Value != null).ToList();

            //prepare the API call request to fetch the response
            HttpRequest _request = ClientInstance.Post(_queryUrl, _headers, _fields, Configuration.BasicAuthUserName, Configuration.BasicAuthPassword);

            //invoke request and get response
            HttpStringResponse _response = (HttpStringResponse)await ClientInstance.ExecuteAsStringAsync(_request).ConfigureAwait(false);

            HttpContext _context = new HttpContext(_request, _response);

            //handle errors defined at the API level
            base.ValidateResponse(_response, _context);

            try
            {
                return(_response.Body);
            }
            catch (Exception _ex)
            {
                throw new APIException("Failed to parse the response: " + _ex.Message, _context);
            }
        }