When paying your bill via BPAY, you will need a biller code and a reference number.
The biller code is one AGL provides, and it depends on your account particulars. The reference number is specific to your account. Refer to the bottom page of your most recent bill, like this to find the biller code:
If you receive your bill via email, you'll find this information in the detailed PDF version of your bill. In the email, click Download your bill (PDF) - you'll be presented with your detailed bill, which includes all relevant payment reference numbers on the bottom of the second page.