The short answer: attach the invoice as a PDF to a short email sent to whoever approves payment. Put the invoice number, your business name and the due date in the subject line, and repeat the amount, the due date and how to pay in the first lines of the email, so it can be approved without opening the attachment. The templates below cover the first invoice through to a final reminder.
Before you press send
- PDF, not Word: it looks the same on every device and can’t be edited by accident. Name it so it can be found:
INV-2026-042_BirchLaneStudio.pdf. - The right person: your project contact often doesn’t release payment. Ask once who invoices go to and whether they need a purchase order number, then send to that address and copy your contact.
- The details they check: their PO number, their legal name and billing address, and your bank details or payment link.
Subject lines
Invoice INV-2026-042 from Birch Lane Studio, due 23 October
Invoice INV-2026-042 for PO 5521: September retainer
Deposit invoice INV-2026-043: kitchen refit, 3 Elm Road
Reminder: invoice INV-2026-042 due Friday 23 October
Overdue: invoice INV-2026-042, due 23 October
Email templates
Replace the bracketed parts. Names and figures are made up.
Hi [Sam],
Please find attached invoice [INV-2026-042] for [the September content retainer], [£2,400.00].
Payment is due by [23 October 2026] by bank transfer; the details are on the invoice.
Thanks,
[Alex]
Hi [Sam],
Thanks for accepting the quote. Attached is the [25%] deposit invoice, [£1,110.00], which confirms your start date of [3 November].
The balance will be invoiced on completion.
[Alex]
Hi [Sam],
Stage [2], [design sign-off], is complete. Attached is invoice [INV-2026-051] for [£3,000.00], due [6 November].
Invoiced so far: [£6,000.00] of [£12,000.00].
[Alex]
Hi [Sam],
Here is the invoice for [October]: [20 hours] of support, [£1,600.00], due [14 November]. A summary of the work is on page 2.
[Alex]
Hi [Sam],
As requested, here is invoice [INV-2026-042] again. Nothing has changed: [£2,400.00], due [23 October]. Please let me know if it should go to a different address.
[Alex]
Hi [Sam],
A quick reminder that invoice [INV-2026-042], [£2,400.00], is due on [Friday]. I have attached it again for convenience.
Thanks,
[Alex]
Hi [Sam],
Invoice [INV-2026-042] for [£2,400.00] was due on [23 October] and is now [7] days overdue. Could you let me know when payment is scheduled? If it has already been sent, please ignore this.
[Alex]
Dear [Sam],
Invoice [INV-2026-042] for [£2,400.00] is now [30] days overdue. Unless it is paid by [date], I will add statutory interest and the fixed compensation that the late payment law allows on business debts.
Kind regards,
[Alex]
Hi [Sam],
Thank you, I have received [£2,400.00] for invoice [INV-2026-042]. It is now marked as paid.
[Alex]
Template 8 is for business customers only. Work out the amounts with the late payment interest calculator: in the UK, statutory interest is 8% plus the Bank of England base rate, and the fixed sum is £40, £70 or £100 depending on the debt (GOV.UK).
A reminder schedule
| When | What to send |
|---|---|
| On the day the work is delivered | Template 1, 2, 3 or 4 |
| 3 days before the due date | Template 6 |
| 7 days after the due date | Template 7, and a phone call if you have a contact |
| 30 days after the due date | Template 8 |
| When paid | Template 9 |
When the client uses a supplier portal
Some larger companies take invoices only through a supplier portal or a procurement system rather than by email. Ask during onboarding, register before you invoice, and quote their purchase order number exactly, because an invoice that doesn’t match the order is often rejected without anyone telling you.
The invoice generator makes the PDF to attach. For what goes on the invoice itself, see how to write a professional invoice.