You can't use [INVOICENUMBER] in "Invoice number format" or "Proforma Invoice number format" as it'd be like trying to substitute itself. The substitutions listed under "Substitutions in Invoice number format" are what is available for usage in the invoice number format parameters. [INVOICENUMBER] is for usage in the "Proforma Invoice title format" and "Invoice title format" parameters specifically, which just displays the formatted invoice number. Additionally [INVOICENUMBER] in "Proforma Invoice title format" will be "Proforma Invoice number format" and not "Invoice number format".