Anybody been able to get a push notification UI content extension to work?

I can successfully get a service extension to work (for both a local notification and a push notification) but I'm not able to get a UI content extension to work.

I created one using the XCode template and haven't editied it beyond that.

Then in my container app I'm doing the following to register a category:

        let customUICategory = UNNotificationCategory.init(identifier: "myNotificationCategory", actions: [], minimalActions: [], intentIdentifiers: [])
        UNUserNotificationCenter.current().setNotificationCategories([customUICategory])

And in the push payload added:

       category: "myNotificationCategory"

The XCode template automatically added the UNNotifictionExtensionCategory key to the extension Info.plist, which has the name "myNotificationCategory".

The push is sucessfully delivered to the device and displayed and a service extension is run but the content extension.

Anybody been playing around with a content extension and managed to get it to work?