The data.relationships.emails.data.0.attributes.email must be a valid email address.
We are receiving this error directly from KWCommand. The app is perventing PieSync from adding the contact to the contacts database because, based on their own validation, it's defined as an invalid email address.
Amend the email address in your other app. Piesync will automatically pick this up and sync the contact across (if KWCommand allows the new email address)
Please reach out to KWCommand directly for more information on email address validations.