Last tested: Dec 28, 2018
One possible reason is that the URL is missing the port number:
https://mycompany.looker.com/api/3.0/login instead of
https://mycompany.looker.com:19999/api/3.0/login . Leaving the port unspecified will use the default port of 443, which isn't used for API calls. Adding
:19999 to the URL should resolve the issue.
This can also happen when using an out of date version of the Ruby gem. Make sure to keep those gems updated. You can check at https://rubygems.org/gems/looker-sdk
This can also happen when you don't include the
/api/<version number>/ portion of the URL. If they try to hit
https://mycompany.looker.com:19999/login, they'll see a 403 response.