Once you’ve fed in your license key, you should be able to install the entire Developer Edition bundle (of which Branches is a part) from the Marketplace (Administration > Marketplace).
That is what I was thinking too, but whenever we run a Sonar for Bamboo job, check the “Auto Branch” option, with “Legacy branching” unchecked, we get an error that says we need to have the plugin. Message is: “to use the property ‘***.branch.name’, the branch plugin is required but not installed”
OK, so it appears we have the LTS edition (sonarqube-6.7.6.zip), that we applied an enterprise license to. I see there is a separate enterprise-edition-6.7.6.zip file that contains the plugins. We’ll download that and give it a try.