HttpClient consume Odata Not Working - xamarin.forms

Question

I use below code to access SAP Odata WebService:
string strUrl = "https://...../HandlingUnitSet?$format=json";
var credentials = new NetworkCredential("user", "usr123");
var handler = new HttpClientHandler { Credentials = credentials };
var client = new System.Net.Http.HttpClient(handler);
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Add("Accept", "application/json");
var response = await client.GetAsync(strUrl);
string status = response.StatusCode.ToString();
string header = response.Headers.ToString();
string cont = response.Content.ToString();
string contactsJson = response.Content.ReadAsStringAsync().Result;
UoUnit ObjUnitList = new UoUnit();
ObjUnitList = JsonConvert.DeserializeObject<UoUnit>(contactsJson);
The Problem : I got the below error message
The url suppose to return Json Data but I did not get it. This error encountered at the line of DeserializeObject
Unexpected character encountered while parsing value: <. Path '', line 0, position 0.
at Newtonsoft.Json.JsonTextReader.ParseValue ()
{Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: <. Path '', line 0, position 0.
at Newtonsoft.Json.JsonTextReader.ParseValue () [0x002b3] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonTextReader.Read () [0x0004c] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonReader.ReadAndMoveToContent () [0x00000] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonReader.ReadForType (Newtonsoft.Json.Serialization.JsonContract contract, System.Boolean hasConverter) [0x0004a] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize (Newtonsoft.Json.JsonReader reader, System.Type objectType, System.Boolean checkAdditionalContent) [0x000db] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonSerializer.DeserializeInternal (Newtonsoft.Json.JsonReader reader, System.Type objectType) [0x00054] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonSerializer.Deserialize (Newtonsoft.Json.JsonReader reader, System.Type objectType) [0x00000] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonConvert.DeserializeObject (System.String value, System.Type type, Newtonsoft.Json.JsonSerializerSettings settings) [0x0002d] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonConvert.DeserializeObject[T] (System.String value, Newtonsoft.Json.JsonSerializerSettings settings) [0x00000] in <d32db49e5e3440729da31845c03ddc3a>:0
at Newtonsoft.Json.JsonConvert.DeserializeObject[T] (System.String value) [0x00000] in <d32db49e5e3440729da31845c03ddc3a>:0
}