Subject: Invoice Due: Reminder | [COMPANY_NAME]
This is a reminder that invoice #[INVOICE_NUMBER] was due on [DUE_DATE] and remains unpaid. I have attached a copy of the invoice to this document.
You can make the payment to the account specified in the invoice. If you want to pay us via other means please contact us.
I would appreciate it if you could treat this matter with utmost priority and settle the outstanding dues immediately.
In the event that you have made the payment, please disregard this email and accept my sincere apologies for the trouble.
Please let me know if you have any questions about the invoice.