The requested URL could not be retrieved with plumber endpoint in QC environment

I have developed API endpoint using R plumber package (https://www.google.com/search?q=plumber+R&rlz=1C1GCEA_enHR855HR855&oq=plumber+R&aqs=chrome..69i57j35i39l2j69i60j69i65j69i60l2.1344j0j15&sourceid=chrome&ie=UTF-8). Endpoint is GET request with 4 query parameters. The endpoint works as expected when I try it on my PC. Then I tried to use it inside Quantconnect framework: https://www.quantconnect.com/docs/algorithm-reference/importing-custom-data

When I use their SubscriptionTransportMedium.RemoteFile method it works as expected, but when I use their SubscriptionTransportMedium.Rest method it returns an error page:

ERROR The requested URL could not be retrieved The following error was encountered while trying to retrieve the URL: http://207.154.227.4/alphar/radf_point?’ target=‘blank’>http://207.154.227.4/alphar/radf_point?

Access Denied.

Access control configuration prevents your request from being allowed at this time. Please contact your service provider if you feel this is incorrect.

Your cache administrator is webmaster.

Generated Tue, 11 May 2021 06:56:39 GMT by qc-gateway (squid/3.5.27)

I ma not sure if the above error is returned because of:

1. my plumber endpoint setup or
2. Digital ocean set up or
3. Quantconnect Rest method?

I don’t know much about networks, so I can’t understand what is the problem. On the community in QC, they said I should add login creds, but I don’t understand why should I do that to make endpoint to work?