Subject: FINAL NOTICE — invoice [#1234], [$AMOUNT+FEES]

Dear [CLIENT NAME],

Despite reminders on [DATE 1] and [DATE 2], invoice [#1234] for
[$AMOUNT] remains unpaid, [X] days past its due date. With accrued
late fees of [$FEE], the balance is now [$TOTAL].

If payment is not received by [DEADLINE — give 7 days], I will have no
choice but to escalate this to [a collections agency / small claims
court], which adds costs for both of us and is a step I'd prefer to avoid.

Payment instructions: [DETAILS]. If payment has crossed this notice,
thank you — no further action is needed.

Sincerely,
[YOUR NAME], [YOUR BUSINESS]
