Final answer:
The primary basis for recording sales transactions and updating the customers accounts receivable subsidiary ledger is the sales invoice.
Step-by-step explanation:
The document that the accounting staff will use as the primary basis for recording sales transactions and updating the customers accounts receivable subsidiary ledger is the sales invoice. A sales invoice is a document that provides the details of a sale, including the quantity, price, and terms of payment. It serves as a record of the transaction and is used to update the relevant financial records.