An example of how to authorize Nylas from .Net

NylasAuthResponse.cs

public async Task<ActionResult> NylasAuthenticationResult(string code)
        {
            using (HttpClient httpClient = new HttpClient())
            {
                httpClient.BaseAddress = new Uri("https://api.nylas.com");
                
                //tried as JSON
                var nylasAuthorizeRequest = new NylasAuthorizeRequest
                {
                    ClientId = "cf7jhxlkkvimkxvd2vnkkzci",
                    GrantType = "authorization_code",
                    Code = code
                };
                var authorizeResponseMessage = await httpClient.PostAsJsonAsync<NylasAuthorizeRequest>("oauth/token", nylasAuthorizeRequest).ConfigureAwait(false);
                
                // tried as x-www-form-encoded
                var postData = new List<KeyValuePair<string, string>>();
                postData.Add(new KeyValuePair<string, string>("client_id", "cf7jhxlkkvimkxvd2vnkkzci"));
                postData.Add(new KeyValuePair<string, string>("grant_type ", "authorization_code"));
                postData.Add(new KeyValuePair<string, string>("code ", code));
                
                HttpContent content = new FormUrlEncodedContent(postData);

                var authorizeResponseMessage = await httpClient.PostAsync("oauth/token", content).ConfigureAwait(false);

                var authorizeResponse = authorizeResponseMessage.Content.ReadAsAsync<NylasAuthorizeResponse>().Result;
            }

            return null;
        }