Can't get StaticPublishingTrigger to work

Silverstripe Version: 5.2

Question:

I’ve followed the instructions for Static Publisher as per silverstripe-staticpublishqueue/docs/en/basic_configuration.md at 6 · silverstripe/silverstripe-staticpublishqueue · GitHub but simply cannot get my data object to trigger any page to publish.

I have the following set up:

use SilverStripe\ORM\DataObject;

class Event extends DataObject {
...
}

use Page;
use SilverStripe\StaticPublishQueue\Contract\StaticPublishingTrigger;

class Trip extends Event implements StaticPublishingTrigger {
    public function objectsToUpdate($context) {
        return Page::get()->First();  // return 1 or an array of multiple publishable objects you would like to regenerate the static cache for
    }

     public function objectsToDelete($context) {
        return 1; // Return 1 or an array of publishable objects for which you would like to purge the statically cached variant
    }
}

plus the following in extensions.yml:

App\Web\Trip:
  extensions:
    - SilverStripe\StaticPublishQueue\Extension\Engine\SiteTreePublishingEngine

Any ideas on what I’m missing would be most welcome!