When a customer chooses to pay using Direct Bank Transfer, the order e-mail confirmation shows the bank code, swift code, etc. they need to use. I have added a field there called reference number that they should use when sending the transfer. I would like the reference number to be their order number. I have tried a few different things, but the order number doesn't show in the e-mail confirmation. This is what I currently have in includes/languages/english/modules/payment/dirbank.php:

define('MODULE_PAYMENT_DIRBANK_TEXT_EMAIL_FOOTER',
"Please use the following details to transfer your total order value:\n\n" .
"\nAccount No.: " . MODULE_PAYMENT_DIRBANK_ACCNUM .
"\nBSB Number: " . MODULE_PAYMENT_DIRBANK_BSB .
"\nAccount Name: " . MODULE_PAYMENT_DIRBANK_ACCNAM .
"\nBank Name: " . MODULE_PAYMENT_DIRBANK_BANKNAM .
"\nReference No: " . $zv_orders_id . );
I am just not sure what to use there to get the order number.

Thanks!