API Permission Denied Group Membership

I have not worked with the RQMUrlUtility. You can however find the documentation for the APIs here https://jazz.net/wiki/bin/view/Deployment/ELMProductAPILanding . The API you want is the Reportable REST API https://jazz.net/wiki/bin/view/Main/RqmApi . I would check if your request would work based on that. Check the request headers etc.

I usually use a REST Client for Firefox (mine is called RESTClient, but there are others), that allows to use the Web UI to authenticate and share the session. Then I create the GET or whatever request. It is a lot easier to see what happens and you do not have to deal with an application in addition.

Group membership usually means the repository role. You need one like JazzUser to be able to access the repository. You also usually need to have a role in the project area. This controls the permissions you have.

I have seen "Your account does not have the group memberships required to access the requested resource". in various contexts. 
1. API calls with incorrect headers
2. Authentication issues
3. LDAP or local user management issues

I would consider it to be the first. You need an Accept header: https://jazz.net/wiki/bin/view/Main/RqmApi#Headers

I have experimented with the EWM Reportable REST API. Some of that should also apply to the ETM API. There are some additional posts around API usage. https://rsjazz.wordpress.com/2022/03/02/ewm-reportable-rest-api/ and check the documentation. Try the simplest request first with a Firefox REST Client. If you know how the authentication works, you can also use Postman. Once you have a working call, use that with the RQMUrlUtility.