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Hello! I'm working on a site that's currently trying to integrate with RingCentral's API. We have multiple customers that will be using the API, so we're going with the Authorization Code Flow. We're able to redirect the user over to RingCentral and have them authorize their account, but when trying to exchange the received code, we receive a 400 error.

The site is an MVC5 app and I haven't been able to find any examples of the authorization code flow for this type of application, but maybe I haven't looked far enough. Below is the bit of code that tries to make the exchange for the access/refresh tokens:

            WebRequest request = WebRequest.Create($"{AppConfig.Settings.RingCentral.ApiEndpoint}/restapi/oauth/token");
            request.ContentType = "application/x-www-form-urlencoded;charset=UTF-8";
            request.Method = "POST";
            request.Headers["Authorization"] = $"Basic {Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes($"{AppConfig.Settings.RingCentral.AppKey}:{AppConfig.Settings.RingCentral.AppSecret}"))}";
            
            string body = $"grant_type=authorization_code;code={code};redirect_uri={AppConfig.Settings.General.RootPublicUrl}/OAuthCallback/RingCentralToken;";

            ASCIIEncoding encoding = new ASCIIEncoding();
            byte[] bytes = encoding.GetBytes(body);
            request.ContentLength = bytes.Length;

            using (var stream = request.GetRequestStream())
            {
                stream.Write(bytes, 0, bytes.Length);
            }

            using (var response = request.GetResponse()) //400 Bad Request here
            {
                //get tokens from response here
            }

I feel like I'm doing something obviously wrong here, but I can't seem to figure out what that is. If I need to give more information, let me know!