HttpClient.SendAsync - The text associated with this error code could not be found. '': Invalid characters found

HttpClient.SendAsync or PostAsync is throwing below error.

System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Exception: The text associated with this error code could not be found.

'': Invalid characters found.
at System.Net.Http.HttpHandlerToFilter.SendAsync(HttpRequestMessage request, CancellationToken cancel)
at System.Net.Http.DiagnosticsHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.HttpClientHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
--- End of inner exception stack trace ---
at System.Net.Http.HttpClientHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts)
at TestApp.MainPage.PostRequest(String url, StringContent stringContent)

Here is the C# Code:

    var address = new AddressModel()
            {
                CommunicationId = "email@domain.com",
                ......
            };
var stringContent = new StringContent(JsonConvert.SerializeObject(address), Encoding.UTF8, "application/json");
HttpClient client = new HttpClient();
client.DefaultRequestHeaders
                          .Accept
                          .Add(new MediaTypeWithQualityHeaderValue("application/json"));//ACCEPT header
                    client.DefaultRequestHeaders.Add("Cookie", AuthCookie);
                    client.DefaultRequestHeaders.Add("X-Requested-With", "X");
                    HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, url)
                    {
                        Content = stringContent//CONTENT-TYPE header
                    };

                        try
                        {
                            //Failing on this Line. 
                            responseMessage = await client.SendAsync(request);
                            if (responseMessage.IsSuccessStatusCode)
                            {
                                var responseContent = await responseMessage.Content.ReadAsStringAsync();
                            }
                        }
                        catch (Exception ex)
                        {
                            //
                        }

Infact, the Post call was successful and response code was 201-created if we observe it in fiddler. but the Json response the post call is returning is causing the error and hence PostAsync is failing to prepare HttpResponseMessage object.

I don't see any issue with the response JSON pasted below which could cause - invalid characters found.

Providing both the Raw request and response.

POST http://host/sap/opu/odata/sap/EMPLOYEE_ADDRESS_SRV/ADDRESS_ODATA HTTP/1.1
Cookie: MYSAPSSO2=---------;
X-Requested-With: X
Accept: application/json
Content-Length: 619
Content-Type: application/json; charset=utf-8
Host: host:8080
Connection: Keep-Alive
Pragma: no-cache

    {"start_date":"20090704","emailid":"email@domain.com","pernr":"123456","subty":"2","begda":"\/Date(1246838400000)\/","endda":"\/Date(1561950000000)\/","stext":"Home","name2":"Xyz","stras":"Address line one","locat":"Address line two","anssa":"1","grpvl":"1","land1":"IN","hsnmr":"2-3","landx50":"India","state":"10","bezei":"Karnataka","ort02":"fsd","ort01":"Bengaluru","entkm":"0","pstlz":"560097","telnr":"1234567890","persg":null,"persk":null,"bukrs":"safs","ename":"afjdsklfsl","persa":null,"molga":null,"country":null,"name1":"asfsd","comp_code":"ABC","emp_curr":"INR","message":"Sample"}

Response:

HTTP/1.1 201 Created
set-cookie: sap-usercontext=sap-client=300; path=/
set-cookie: SAP_SESSIONID_DHR_100=asjkfhskdhfks%3d; path=/
content-type: application/json; charset=utf-8
content-length: 1117
location: http://host:8080/sap/opu/odata/sap/EMPLOYEE_ADDRESS_SRV/ADDRESS_ODATA(emailid='email@domain.com',pernr='123456',subty='2',seqnr='000',start_date='20090704')
dataserviceversion: 2.0
message type: S
custom message: Home has been created successfully
sap-processing-info: ODataBEP=,crp=,st=,MedCacheHub=SHM,codeployed=X,softstate=
sap-perf-fesrec: 232519.000000

    {"d":{"__metadata":{"id":"http://host:8080/sap/opu/odata/sap/EMPLOYEE_ADDRESS_SRV/ADDRESS_ODATA(emailid='email@domain.com',pernr='123456',subty='2',seqnr='000',start_date='20090704')","uri":"http://host:8080/sap/opu/odata/sap/EMPLOYEE_ADDRESS_SRV/ADDRESS_ODATA(emailid='email@domain.com',pernr='123456',subty='2',seqnr='000',start_date='20090704')","type":"EMPLOYEE_ADDRESS_SRV.ADDRESS_ODATAType"},"emailid":"email@domain.com","pernr":"123456","subty":"2","seqnr":"000","start_date":"20090704","begda":"\/Date(1246838400000)\/","endda":"\/Date(1561939200000)\/","stext":"Home","stras":"Address line one","locat":"Address line two","anssa":"1","grpvl":"1","name2":"Xyz","hsnmr":"2-3","ort01":"Bengaluru","ort02":"fsd","pstlz":"560097","land1":"IN","landx50":"India","telnr":"1234567890","entkm":"0","state":"10","bezei":"Karnataka","persg":"","persk":"","bukrs":"safs","ename":"afjdsklfsl","persa":"","molga":"","country":"","name1":"asfsd","comp_code":"WST","emp_curr":"INR","message":"Sample"}}

Solution

Thanks everyone for responding and providing suggestions.

The issue was with the response header properties

message type: S
custom message: Home has been created successfully

key's has space in them. after changing them to message-type and custom-message with hiphen instead of space - it worked fine.