You have configured SonarQube correctly. Without being a NGINX expert, I can tell the problem lies in your Nginx configuration and the location “/” that you have configured. This is out of SonarQube scope and what we can help you with.
I can for sure confirm that your SonarQube Web Server is listening on http://127.0.0.1:8080/sonar, but Nginx is not matching and forwarding the request upon you hitting https://<our domain>/sonar as you are expecting. It is probably handing the request directly to http://127.0.0.1:8080 instead. I would advice reading the Beginner’s Guide of NGINX on the “location” syntax. They have very good examples.