How do I validate ABN in Magento for B2B customers?

ABN (Australian Business Number) validation is critical for B2B Magento stores so you can skip GST on tax-invoice flows where the buyer is a registered business. Two approaches: (1) Live lookup via the ABR (Australian Business Register) web service, we wire an extension or custom module that calls abr.business.gov.au/json/AbnDetails.aspx at registration / checkout, validates the ABN, and stores the verified entity name. (2) Offline checksum validation using the ABN modulo-89 algorithm for instant client-side validation before the live lookup. We typically combine both: instant feedback on the form, live verification before order placement. Combine with a customer attribute `is_abn_verified` and a customer-group rule to expose B2B catalogues / Net-30 terms only to verified ABNs.