Before you can pay anyone, SAP needs to know who they are. That information lives in the vendor master (in S/4HANA the unified term is business partner, often called the supplier master). Every invoice, payment, and report in AP depends on this data being accurate.

A vendor master record is organized into three levels:

• General data — valid across the whole company: name, address, country, tax numbers, and the business partner number itself. This is shared by every company code.
• Company code data — financial settings specific to one of your legal entities. The most important field here is the reconciliation account, the G/L account that automatically receives the offsetting posting whenever you post to this vendor. Payment terms and a default payment method also live here.
• Purchasing data — relevant when the vendor is used in procurement, holding the purchasing organization, order currency, and terms used on purchase orders.

Key fields an AP clerk relies on every day include payment terms (which drive the due date and any cash discount), bank details (account or IBAN, needed for electronic payment), payment method (check, bank transfer, etc.), and the reconciliation account.

To view or maintain a supplier in S/4HANA you use transaction BP (Business Partner). In older ECC systems the classic codes were XK01/XK02/XK03 to create, change, and display a vendor centrally, or FK01/FK02/FK03 for the accounting view only.

Good practice includes segregation of duties — the person who creates or changes a vendor's bank details should not also release payments — and review of any duplicate vendors, which are a common source of duplicate payments and fraud.