Go to WP Admin Dashboard → WP ERP → Accounting → Expenses.
On the Expenses page, to approve any payment click Pay Now.
To deny payment, press Void.
To make changes, press Edit.
On the Sales page, to move something from the draft click on Submit for approval
To take payment, click on Receive payment.
To reject, click Void.
That's how you can approve and void expenses in the Accounting module.