Backend resource plugin - debugging for callResourceHandler "Plugin not registered"

I’m really struggling to get anything more helpful than a single error message when calling /api/plugins/appname/resources

Looking at the docs for it seems that it should be possible to implement an HTTP handler that is not specifically a datasource, by satisfying backend.CallResourceHandler interface and passing it in backend.ServeOpts to backend.Serve()

t=2020-10-15T05:59:17+0000 lvl=eror msg="Failed to call resource" logger=context userId=0 orgId=1 uname= error="Plugin not registered"
t=2020-10-15T05:59:17+0000 lvl=eror msg="Request Completed" logger=context userId=0 orgId=1 uname= method=GET path=/api/plugins/myplugin/resources/test status=500 remote_addr= time_ms=37 size=37 referer=

The plugin.json has the type set to “app” and “backend”:true and a value for “executable”
mage builds it sucessfully

On launch - grafana debug shows the plugin is found , has no signature (I have configured grafana.ini to allow this) , there is an info message saying the plugin is registered but the executable does not appear to be running.

Any suggestions to get closer to the problem would be a big help.

It turns out that setting the plugin type to “datasource” - the plugin loads sucessfully and my resource endpoint response in the way I had hoped.