You can insert your business number (ABN, ACN, RN, BN, etc.) directly into a blog post, product page, or content page by using the Shortcodes feature built-into Ozcart. At the place where you want the business number to appear, write [abn] and leave it at that. The cart will do the rest and replace this code with the business number that you've set under Configuration > Store Settings > General Settings > Store.
