Asset handle for lightbox

My websites make extensive use of the Webli Adons which in turn use Magnifc lightbox. The Webli addons for Popup images, YouTube and Vimeo videos seem to be no longer supported. I have been working on them and have corrected a number of problems, undefined array keys, variables not declared but am stuck at loading the asset itself:

The code is


however the logs table tells me that this is not a valid asset group handle. I have looked at A list of all assets and asset groups defined by Concrete CMS and this shows core/lightbox. I can find no other reference. Does anyone know what I should be using and how I can find a definitive mapping of assets to their handles?

If you are using Concrete v9 and are in a block’s controller, you should use

     * {@inhertdoc}.
    public function getRequiredFeatures(): array
        return [

Thanks for this. IS there any specific area in the Documentation that shows how this works and how it differs from older versions of Concrete with perhaps some example code?

See Conversation Block in Custom Theme Showing Error - #3 by JohntheFish