I can easily set a service from GitHub to Jenkins webhook in freestyle jobs, but the same doesn't seem to work when the Jenkins job type is an instance of a job template.
I created an attribute in my template called GITHUB_PROJECT_URL and added this xml to the general job definition:
<com.coravy.hudson.plugins.github.GitHubProjectProperty plugin="github@1.18.2">
<projectUrl>${GITHUB_PROJECT_URL}</projectUrl>
<displayName/>
</com.coravy.hudson.plugins.github.GitHubProjectProperty>
and the GitHub link does show up in the sidebar of the template instance (so the attribute works), but testing from the GitHub side doesn't work. I've used the exact same github-webhook URL that works for other job types.
Using Jenkins 1.625.16.1