Only active or expired Pay Now links can be renewed.
Select Billing > Invoices. Highlight the invoice and select APX button and select Renew Pay Now OR right-click the Pay Now invoice and select Renew Pay Now. Select the APX account when prompted and select Accept. The Create Notes window opens where you can edit the email as you like and select OK to send. Complete the final email and send it, the invoice is then resent as a Pay Now email with a renewed link.