How to make payment to Staff for rendered services via PayPal?

To make a payment against an owed invoice to a Staff member you must go to "Invoices" > "Manage" and then search the staff member applicable.

Alternatively you can select  "Show Staff Earnings Invoices Only" and "Show Unpaid Invoices Only" and search by this. 

Go in to the applicable invoice and scroll to the bottom of the page and hit the "Buy Now" PayPal button.

Make payment via PayPal as usual and hit the final "Return to Merchant" button at the final stage.

Once you return, payment will be sent an the invoice will be marked as paid in the Payments section as demonstrated below: