As a developer creating statistics tools, chat bots, overlays and loyality tools, i also would like to add bits spent to those tools, which were obtained through extensions, for example Sound Alerts or Stream Stickers.

I would suggest adding a new field "isextensionbits" being true or false in the notification body (or, as an alternative, have a seperate notification type to not confuse existing apps, like channel.cheer.extension)