Radarr/Radarr · error · DownloadClientException

Failed to connect to qBittorrent, check your settings.

Error message

Failed to connect to qBittorrent, check your settings.

What it means

Thrown by the qBittorrent v2 API support probe (IsApiSupported) when the response has an HTTP error status (HasHttpError) that is not 404, 403, or 401 (the special-cased statuses). It is the generic HTTP-error fallback for the v2 support check, wrapping the response in an HttpException.

Source

Thrown at src/NzbDrone.Core/Download/Clients/QBittorrent/QBittorrentProxyV2.cs:55

                // Version request will return 404 if it doesn't exist.
                if (response.StatusCode == HttpStatusCode.NotFound)
                {
                    return false;
                }

                if (response.StatusCode == HttpStatusCode.Forbidden)
                {
                    return true;
                }

                if (response.StatusCode == HttpStatusCode.Unauthorized)
                {
                    throw new DownloadClientException("Failed to connect to qBittorrent. Check your settings and qBittorrent configuration.", new HttpException(response));
                }

                if (response.HasHttpError)
                {
                    throw new DownloadClientException("Failed to connect to qBittorrent, check your settings.", new HttpException(response));
                }

                return true;
            }
            catch (WebException ex)
            {
                if (ex.Status == WebExceptionStatus.TrustFailure)
                {
                    throw new DownloadClientUnavailableException("Unable to connect to qBittorrent, certificate validation failed.", ex);
                }

                throw new DownloadClientException("Failed to connect to qBittorrent, check your settings.", ex);
            }
        }

        public Version GetApiVersion(QBittorrentSettings settings)
        {
            var request = BuildRequest(settings).Resource("/api/v2/app/webapiVersion");

View on GitHub (pinned to ca451608dc)

Solutions

Confirm the qBittorrent Web UI is healthy by opening it in a browser.
Check qBittorrent logs for 5xx errors on the API path.
Verify the reverse proxy (if any) forwards the v2 API path correctly.
Re-test the connection after qBittorrent has fully started.

Defensive patterns

Strategy: try-catch

Try / catch

try
{
    var supported = proxyV2.IsApiSupported(settings);
}
catch (DownloadClientException ex)
{
    logger.Warn(ex, "qBittorrent v2 API probe returned an unexpected HTTP error.");
}

Prevention

Confirm the qBittorrent Web UI is healthy (open it in a browser).
Check qBittorrent logs for 5xx on the API path.
Re-test after qBittorrent has fully started.

When it happens

Trigger: In QBittorrentProxyV2.IsApiSupported, response.HasHttpError is true and the status is none of NotFound, Forbidden, or Unauthorized.

Common situations: qBittorrent Web UI returned a 5xx on the API endpoint (overloaded/crashing); a reverse proxy gateway error (502/504); the request hit an unexpected redirect or status from a misconfigured setup.

Related errors

AI-assisted analysis of Radarr/Radarr@ca451608dc (2026-08-13). Data as JSON: /api/errors/64716c176f02f1e0. Report an issue: GitHub.