iPhone Sound alert for Fantastical — horribly confusing

I've switched off sound for Fantastical2 and kept banners as their guidelines suggested. Disabled banner and switched on sound notifications for the default calendar BUT I'm getting some other pissweak sound alert. Where the heck is that coming from?

Can anyone at all post a link to a straightforward guideline that keeps to the point without trying to glamor me with hype about iOS THAT explains how to set the default calendar sound so that it works. Something is overriding — trying for over an hour.