Today I got the
The Push Notifications feature is not activated on the site.
quite quickly I got an article describing what to do. I had however the same problem as others. I’m on office 365.
Easy solution: OfficeDev/PnP-PowerShell on Github has Enable-SPOFeature available.
Connect-SPOnline https:/ /mytenant.sharepoint.com Enable-SPOFeature -Identity 41e1d4bf-b1a2-47f7-ab80-d5d6cbba3092