Email to a client who has not paid

Write a 90-word email to [a client] who has not paid invoice [No. 214] for [€480], due [12 October]. Rules: 1) state the invoice number, amount and original due date in the first two lines, 2) assume a mistake first — one friendly sentence, no accusation, 3) ask for payment by [a date 7 days from now] to [bank account or payment link], 4) say what happens if I hear nothing, in one calm sentence [I will send a final reminder on that date]. No threats, no legal words, no apologies for asking. Start with the result itself — no introduction, no summary at the end.