The auto replay feature is smart enough to reattempt the action within a Zap immediately after a failure.
After the first failure, it will wait before re-attempting a send. This means whether the cause of the error was a minor issue or an outage of 6 hours, Zapier will be able to reply the task as soon as the error is resolved.
In some cases however, a task may never complete – in this instance an error email will be sent giving the user the opportunity to manually replay the task from within task history.
To enable autoreplay follow this helpful guide from Zapier.