Subject: Please see the attached open invoice(s)
Dear <First>,
 
I've attached a copy of your open invoice(s). If you have any questions, please let me know.
 

Your invoices are now available to be paid online, please click on the following button to log in to your account:

Account Login
 
Thank you for doing business with [Success Press]. We look forward to serving you again.

Sincerely,
 
<CSR>

[Success Press]
Phone [(555) 123-4567]
www.[successpress.com]