I have a paid actor and I have set up a scheduled task to daily check if it works for my customers. Will I automatically get an email if the run fails?
If the actor runs under your account you would get an email about successfull or failed run. If the actor is not running on your account you may setup an API call for https://apify.com/apify/send-mail actor, which would send you an email. (check integration tab on the actor -> add integration -> and HTTP Webhook)
No, I do not think so. I was searching for that feature not so long ago and did not found anything. But webhook that runs the send-mail actor is good enough.
I do not know how to trigger failed run. But you can test it with aborted run first. It is pretty good chance that it will work with failed if it works with aborted