Glad to know it helped 
So it was this point:
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- UiPath’s Marketplace Feed (https://gallery.uipath.com/api/v3/index.json ) as a package source in Visual Studio. See here for instructions on adding package sources.
We’ve had the exact same error at one point. Thank you also for documenting here in this topic. I’m sure this will help others on the path of creating their own custome activities!
Thanks and hopefully we meet again in another Community Meetup.