Hey Alberto! Sorry that you're having some trouble (but thanks for reading the manuals first! ).
So, the line that says "PostgreSQL repository returned 0 rows " means that VizAlerts can query your PostgreSQL repository without issue, but it's finding no valid alerts to process. That is usually due to a problem with the way the Schedules were set up. Do their names conform to the pattern VizAlerts is looking for in the SQL query at the bottom of your vizalerts.yaml file? Did you make sure they were Subscriptions schedules, and also that they were set to Disabled in Tableau Server? Are there any subscriptions on those Schedules right now?
If the answer to all three is "yes", then if you could attach the SQL query at the bottom of your yaml file (don't send any passwords please!) and a screenshot of your VizAlerts schedules, I'll take a look and see if I can figure out what's up.