Notification email was not sent

Dear Sir,

I can’t find a useful doc from the wp plugin site.
Can anyone guide me how to configure the email notification correctly?

I got below error messages when I upload file (already enable email notification in settings).

“Notification email was not sent due to an error. Please check notifyrecipients, notifysubject and notifymessage attributes for errors.”

Below settings I configured in settings:
Email Recipients [email protected]
Email Headers (empty, not set)
Email Subject xxxxxx (just some text)
Email Body xxxxxx (just some text)
Attach Uploaded Files – ON

Thank you!