MS Dynamics 365 - Create records using ms dynamics Web API

        public static string CreateLead(string accessToken , string countryid, string userid)
        {
            string leadUri = string.Empty;
            try
            {
                JObject leadObj = new JObject { };
                leadObj["firstname"] = "Prasad";   // text field
                leadObj["lastname"] = "Testing";  // text field
                leadObj["srin_leadsource"] = 1;         // Option set
                leadObj["srin_Country@odata.bind"] = "/srin_countries(" + countryid + ")"; //  Set custom lookup value
                leadObj["ownerid@odata.bind"] = "/systemusers(" + userid + ")";              // Set OOB lookup Value

                leadUri= Task.Run(async () => await CallDynamicsAPI(accessToken, "leads", leadObj)).Result;
            }
            catch (Exception ex)
            {

                throw;
            }
            return leadUri;
        }

To create access token/authToken please go through my previous post from the below URL.

http://www.dotnetfunda.com/codes/show/8371/ms-dynamics-365-consume-dynamics-web-api-from-csharp

Note : Copy entity and field names using CRM Rest Builder because web api will throw an error if we use entity display / schema names.

 public static async Task<string> CallDynamicsAPI(string accesToken, string entityName, JObject entityObject)
        {
            
            string apiUrl = "https://xyka12.api.crm8.dynamics.com/api/data/v9.1/";
            string recordUri = "";
            HttpClient client = new HttpClient();
            client.Timeout = TimeSpan.FromSeconds(360);
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accesToken);
            client.BaseAddress = new Uri(apiUrl);
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            client.DefaultRequestHeaders.Add("OData-MaxVersion", "4.0");
            client.DefaultRequestHeaders.Add("OData-Version", "4.0");
            client.DefaultRequestHeaders.Add("Cache-Control", "no-cache");

            HttpRequestMessage createHttpRequest = new HttpRequestMessage(HttpMethod.Post, apiUrl + entityName);
            createHttpRequest.Content = new StringContent(entityObject.ToString(), Encoding.UTF8, "application/json");
            var response = await client.SendAsync(createHttpRequest);
            response.EnsureSuccessStatusCode();

            if (response.StatusCode == HttpStatusCode.NoContent)
            {
                recordUri = response.Headers.GetValues("OData-EntityId").FirstOrDefault();
                Console.WriteLine("Record URI: {0}", recordUri);
                Console.WriteLine("Record created in MS Dynamics.");              
            }
            return recordUri;
        }