Here's how to test this:
1) If you're logged into Tableau Server in your web browser then log out.
2) Log into Tableau Server with the same username that you set up in the vizalerts.yaml file server.user setting.
3) Paste the URL you got in the error message into your browser. One of two things will happen:
3.a) You get a "not found" error. In that case here are some possible causes:
3.a.1) The VizAlertsConfig/ScheduledTriggerViews viz has not been published to Tableau Server, you'll need to go back a few steps in the instructions to see that.
3.a.2) The ScheduledTriggerViews viz was published to some site other than default and the vizalerts.yaml file vizalerts.source.site setting wasn't updated.
3.a.3) The ScheduledTriggerViews viz was published with a different workbook and/or worksheet name and the vizalerts.yaml file vizalerts.source.viz setting wasn't updated.
3.a.4) It could be that the ScheduledTriggerViews viz was published but the server.user doesn't have permissions on the viz, though if my memory serves me a different error message would be issued in that case.
3.b) The ScheduledTriggerViews viz renders as a csv. In that case double-check steps #1 and #2 above that you are really using the same login, if you are then you should be getting a "not found" error. If the view does render as a CSV at that point then I'm not sure what might cause the error because there's so much that has to be working to get to the point of downloading a viz (there are permissions for VizAlerts to reach the Tableau Server, a trusted ticket has been issued, and so on), we'd need to do more research.
Let us know how it goes!
Thank you Jonathan!
The error was around the workbook not being published with the correct name.