@markgrant Your TopBox is empty:
You have not put any content inside the lightbox, so it opens with only the white border showing:
If you want content shown in this view (like your ‘4 new sticker packs for your chats’ image), you need to select the appropriate content type in the TopBox settings (e.g. image) and add the content in edit mode, into the ‘lightbox’ placeholder.
The documentation and tutorial video for TopBox make this stack remarkably easy to use, so I’d suggest you take a look at those free resources again.
I’m not seeing anything wrong with your setup based on what I can see at this end; other than you’ve not completed the configuration of your TopBox stack yet. Put some content in the lightbox, and it will work just fine.