Accounts payable process is required in a company because this will help and guide the accountant to manage their payables with in the normal course of the business.
This includes verifying and checking the invoice details including the credit terms, due date, mode of payment, payee and the items received. Only the items received will be paid. Incase theres a discrepancy against the actual receipts, a credit note will be raised by the supplier against the short-shipped invoice.
At the end of the month, AP reconcilition is required confirming both parties balances thru the statement of accounts (SOA). This you can identify which invoices or payment hasnt been booked yet by both parties and you will end up with the same balances, (equal balance from your company and with their company).