'Automated Email Failed' error on Sales Engagement targets

There are multiple reasons that an automated email can fail, follow the steps below to resolve the behavior, or get more detailed error information:
 

1. Check the Sales Engagements component and click View Steps to see if an error is available.
2. If Inbox is enabled in the organization, confirm that the user that was assigned the prospect has connected their email account. An easy way to confirm this is to have the user access the prospect record, then click the Email quick action. If they haven't yet connected their account they will be prompted to do so here.
3. Have the user that was assigned the prospect click Send Manually in the Sales Engagements lightning component on the prospect. You may need to edit the lightning page to add the component for your users. If the email fails when using Send Manually, the more detailed error information may be presented. For example, an error may indicate that there's an issue with the prospect record, a problem with the Email template selected for the Sales Cadence Step, etc.
4. If, when attempting to Send Manually, the user must confirm that the prospect "wants non-commercial emails only", this indicates that the Email Opt Out field on the prospect has been set to True. Automated Email steps will fail for prospects that have opted out of email.
5. Have the user that was assigned the prospect confirm that they're able to send email outside of the Sales Cadence. To do so, the user can click the Email quick action on a prospect record to send a test email. It may be best to create a test record with an internal email address to test this behavior. If they are able to send an email to the test record, add it to the Sales Cadence to see if it also fails to send an automated email.

If you're still unable to determine why the error is presented, please create a support case through Salesforce Help.