Subject: Payment reminder — invoice [invoice number]

Hi [client name],

I’m following up on invoice [invoice number] for [currency and amount], which was due on [due date]. Our records currently show [remaining amount] outstanding.

Could you confirm the expected payment date? If payment has already been sent, please share its date and reference so we can match it to the invoice.

I’ve included [the invoice / a copy of the statement] for reference. Please let me know if anything needs clarification.

Thank you,
[your name]