This article explains the self registration options for the Customer Portal
Portal Self-Registration Options
ZipCode: Is the zipcode on the AR customer address page in Sage for the associated customer.
Email: Is the email address on the AR customer address page in Sage for the associated customer.
Last Payment Amount: Is the most recent receipt received in AR posted/unposted for the associated customer.
Last Invoice Number: Is the invoice number of the most recent invoice posted/unposted in AR and OE for the associated customer.
Last Invoice Date: Is the invoice date of the most recent invoice posted/unposted in AR and OE for the associated customer.