To sync the order with this error, you can restore the contact in Xero which is associated with the order and then click on "Resync Order" button from the Order List >> Unsynced orders page of our app.
To restore a contact archived in Xero, you can navigate to Contacts menu >> All contacts >> Archived tab >> Click on the contact to open their details >> Click Restore
OR
You can contact our support team at apps@parextech.com or from the Contact Us page of this site. Our team can remap the contact and sync the order.