Adding a playground file to a Figma plugin – any luck?

Hi! Yesterday (11/29) Figma added the ability to add a playground file to your Figma plugin, which will open in a new tab when someone decides to “Try Out” your plugin.

Has anyone had any luck adding a playground file to a plugin? The help doesn’t say how to do it, just that you can “choose” one. Is this supposed to be saved as a .fig file first? I try clicking on the Upload button in the Publish popup (see below), and it just dismisses the popup.

Also, clicking the “use our template” link goes nowhere and does not open a browser tab; it does nothing at all.

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Has anyone had any luck with this?

MacOS 12.5 (Intel chipset), desktop Figma app version 116.5.18