Quickbooks can throw a somewhat confusing error when attempting to load information including email addresses. The QBO system attempts to verify that any information entered as an email address is a valid address, but when it doesn’t like an address, the response it gives is confusing. Most users aren’t going to know what RFC 822 is…
Typically, this happens when attempting to upload invoices for a customer where there is no email address entered into the Quickbooks system. Amalgam’s sheet will attempt to search for that customer’s default email, an if it comes up with nothing it might put a zero in the email field. Quickbooks will (correctly) identify that zero is not a valid email address.
To resolve this problem, double check that all of your invoices contain valid customers, and delete any rows where something other than a real email address is entered in the email column.