Hi! Hmm. A 405 “Method not allowed” would usually indicate you are doing something other than GET to try to retrieve this from the API. For example, POST, PUT, etc. wouldn’t be accepted.
Now, once you are beyond that you can pull just the specific group by name using the “q” parameter, the fourth one in your list from above. That looks for the group name using a “starts with” operation.
Now, for the final part of your question, to get the users from a particular group look in the “_links” section of the JSON response and grab the “users” value as the link to use. If you peek at it you will see it has the GUID for the group in the URL, so if you knew that before you could skip my middle step