Failure to create notifications in ArcGIS Monitor for existing emails, with returns the error, "Validation Exception email: unique validation failed on email".

Workaround

Type a portion of the username or email address of a Monitor user account, then click the user to add them as a recipient. Refer to this documentation https://doc.arcgis.com/en/monitor/latest/get-started/windows/create-notifications.htm) for guidance.

Steps to Reproduce