[INVOICEVAT] - invoice sum of all vat value
[INVOICEUPSELL0] - base price without upsell items or other charges added later
[INVOICEUPSELL1] - value of upsell item 1 (number can be between 1 to 20)
[INVOICEUPSELLQTY1] - quantity of upsell item 1 (number can be between 1 to 20)
[INVOICEEXTRAITEM1] - value of extra invoice item 1 (number can be between 0 to 20)
[INVOICEEXTRAITEM1] - value of extra invoice item 1 (number can be between 0 to 20)