Token refreshing C#

When i run my app, the Run task is probably stopping at some point as when i try to acces dropbox files it throws out a NullReferenceException of the DropboxClient and i have no clue on how to get the refresh token. Also the ApiKey and ApiSecret are replaced in my code.

Here is what i have inside my app so far:

public partial class RWindow : Form
    {
        //Dropbox stuff
        private const string ApiKey = "";

        private const string ApiSecret = "";

        private const string LoopbackHost = "http://127.0.0.1:52475/";

        // URL to receive OAuth 2 redirect from Dropbox server.
        // You also need to register this redirect URL on https://www.dropbox.com/developers/apps.
        private static readonly Uri RedirectUri = new Uri(LoopbackHost + "authorize");

        // URL to receive access token from JS.
        private static readonly Uri JSRedirectUri = new Uri(LoopbackHost + "token");

        static DropboxClient dbx;
        private List<string> fileNames = new List<string>();
        private string folder;


        public RWindow()
        {
            InitializeComponent();
            var task = Task.Run((Func<Task>)Run);
            task.Wait();
        }

        static async Task Run()
        {
            DropboxCertHelper.InitializeCertPinning();

            string[] scopeList = new string[3] { "files.metadata.read", "files.content.read", "account_info.read" };
            var uid = await AcquireAccessToken(scopeList, IncludeGrantedScopes.None);
            if (string.IsNullOrEmpty(uid))
            {
                return;
            }

            var httpClient = new HttpClient(new WebRequestHandler { ReadWriteTimeout = 10 * 1000 })
            {
                Timeout = TimeSpan.FromMinutes(20)
            };

            try
            {
                var config = new DropboxClientConfig("SimplePKCEOAuthApp")
                {
                    HttpClient = httpClient
                };

                dbx = new DropboxClient(Settings.Default.RefreshToken, ApiKey, config);

                await dbx.RefreshAccessToken(scopeList);
                await AcquireAccessToken(scopeList, IncludeGrantedScopes.User);

                dbx = new DropboxClient(Settings.Default.AccessToken, Settings.Default.RefreshToken, ApiKey, ApiSecret, config);
            }
            catch (HttpException e)
            {
                Debug.WriteLine("Exception reported from RPC layer");
                Debug.WriteLine("    Status code: {0}", e.StatusCode);
                Debug.WriteLine("    Message    : {0}", e.Message);
                if (e.RequestUri != null)
                {
                    Debug.WriteLine("    Request uri: {0}", e.RequestUri);
                }
            }
        }

        private static async Task HandleOAuth2Redirect(HttpListener http)
        {
            var context = await http.GetContextAsync();

            // We only care about request to RedirectUri endpoint.
            while (context.Request.Url.AbsolutePath != RedirectUri.AbsolutePath)
            {
                context = await http.GetContextAsync();
            }

            context.Response.ContentType = "text/html";

            // Respond with a page which runs JS and sends URL fragment as query string
            // to TokenRedirectUri.
            using (var file = File.OpenRead("index.html"))
            {
                file.CopyTo(context.Response.OutputStream);
            }

            context.Response.OutputStream.Close();
        }

        private static async Task<Uri> HandleJSRedirect(HttpListener http)
        {
            var context = await http.GetContextAsync();

            // We only care about request to TokenRedirectUri endpoint.
            while (context.Request.Url.AbsolutePath != JSRedirectUri.AbsolutePath)
            {
                context = await http.GetContextAsync();
            }

            var redirectUri = new Uri(context.Request.QueryString["url_with_fragment"]);

            return redirectUri;
        }

        private static async Task<string> AcquireAccessToken(string[] scopeList, IncludeGrantedScopes includeGrantedScopes)
        {
            Settings.Default.Reset();

            var accessToken = Settings.Default.AccessToken;
            var refreshToken = Settings.Default.RefreshToken;

            if (string.IsNullOrEmpty(accessToken))
            {
                try
                {
                    Debug.WriteLine("Waiting for credentials.");
                    var state = Guid.NewGuid().ToString("N");
                    var authorizeUri = DropboxOAuth2Helper.GetAuthorizeUri(OAuthResponseType.Code, ApiKey, RedirectUri, state: state, tokenAccessType: TokenAccessType.Offline, scopeList: scopeList, includeGrantedScopes: includeGrantedScopes);
                    var http = new HttpListener();
                    http.Prefixes.Add(LoopbackHost);

                    http.Start();

                    System.Diagnostics.Process.Start(authorizeUri.ToString());

                    // Handle OAuth redirect and send URL fragment to local server using JS.
                    await HandleOAuth2Redirect(http);

                    // Handle redirect from JS and process OAuth response.
                    var redirectUri = await HandleJSRedirect(http);

                    var tokenResult = await DropboxOAuth2Helper.ProcessCodeFlowAsync(redirectUri, ApiKey, ApiSecret, RedirectUri.ToString(), state);
                    accessToken = tokenResult.AccessToken;
                    refreshToken = tokenResult.RefreshToken;
                    var uid = tokenResult.Uid;
                    Debug.WriteLine("Uid: {0}", uid);
                    Debug.WriteLine("AccessToken: {0}", accessToken);
                    if (tokenResult.RefreshToken != null)
                    {
                        Debug.WriteLine("RefreshToken: {0}", refreshToken);
                        Settings.Default.RefreshToken = refreshToken;
                    }
                    if (tokenResult.ExpiresAt != null)
                    {
                        Debug.WriteLine("ExpiresAt: {0}", tokenResult.ExpiresAt);
                    }
                    if (tokenResult.ScopeList != null)
                    {
                        Debug.WriteLine("Scopes: {0}", String.Join(" ", tokenResult.ScopeList));
                    }
                    Settings.Default.AccessToken = accessToken;
                    Settings.Default.Uid = uid;
                    Settings.Default.Save();
                    http.Stop();
                    return uid;
                }
                catch (Exception e)
                {
                    Debug.WriteLine("Error: {0}", e.Message);
                    return null;
                }
            }

            return null;
        }
//Rest of my code that handles requesting and downloading files stored in the application. Works properly when using the generated short-lived token in app console.
}