Delphi/Android application error : "Unsupported Media Type"

I made a multi-platform applet with Delphi 11.3. I'm using the TNetHTTPClient component to POST an XML formatted text to a REST API. Running it in Win32 mode works fine. Running it in Android mode throws an error:

Unsupported Media Type

Here is the code:

procedure TForm13.Button1Click(Sender: TObject);var  HttpClient: TNetHTTPClient;  Response: IHTTPResponse;  URL,user,key,XML, AFM: string;  s, F : TstringStream;  FormData: TMultipartFormData;  XMLData: TBytesStream;  PostData: TBytes;begin  HttpClient := TNetHTTPClient.Create(nil);  try      URL := 'https://www1.gsis.gr/wsaade/RgWsPublic2/RgWsPublic2?WSDL';      XML := '<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope" xmlns:ns1="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" xmlns:ns2="http://rgwspublic2/RgWsPublic2Service" xmlns:ns3="http://rgwspublic2/RgWsPublic2">'+'<env:Header>'+'<ns1:Security>'+'<ns1:UsernameToken>'+'<ns1:Username>username</ns1:Username>'+'<ns1:Password>key</ns1:Password>'+'</ns1:UsernameToken>'+'</ns1:Security>'+'</env:Header>'+'<env:Body>'+'<ns2:rgWsPublic2AfmMethod>'+'<ns2:INPUT_REC>'+'<ns3:afm_called_by/>'+'<ns3:afm_called_for>'+AFM+'</ns3:afm_called_for>'+'<ns3:as_on_date>'+formatDateTime('yyyy-mm-dd',date)+'</ns3:as_on_date>'+'</ns2:INPUT_REC>'+'</ns2:rgWsPublic2AfmMethod>'+'</env:Body>'+'</env:Envelope>';            s := TstringStream.create(UTF8encode(XML));       Response := HttpClient.Post(URL, s, nil); // succeeds in win32, fails in Android     //  Response := HttpClient.Post(URL, s, nil, [TNetHeader.Create('Content-Type', 'text/xml')]); // fails in both platforms    if Response.StatusCode = 200 then    begin      Memo1.Lines.Text := Response.ContentAsString();    end    else    begin      ShowMessage('Error: '+ Response.StatusCode.ToString +' - '+ Response.StatusText);    end;  finally    HttpClient.Free;  end;end;

I have tried to post as TMultipartFormData or as XMLData := TBytesStream.Create(TEncoding.UTF8.GetBytes(XML)) or as Response := HttpClient.Post(URL, s, nil, [TNetHeader.Create('Content-Type', 'text or application/xml')]) but it always fails.