"HTTPError generating trusted ticket: Not Found" means that VizAlerts cannot even talk to your Tableau Server instance. It's a little misleading that the trusted ticket test is what fails, because it isn't really an issue with the ticket itself, but a more basic problem of utterly failing before it even got the chance to ask for one.
So, check your config\vizalerts.yaml file, specifically the server and server.ssl settings. Does your server use SSL? If not, and you're yaml says you are, then it will fail. Does your server require SSL? If so, and your yaml file says false, then it will fail. Make sure you can connect to the server from the machine your trying to run VizAlerts on too, just to rule out any firewall issues or other connectivity issues.
Note that once you solve this issue, others typically find other problems in their config, so you might check out these threads:
VizAlerts 2.0.1 Released (someone posted their issues in that thread)