Late invoice reminder emails for an architecture firm: five templates
https://archon-partners.com/guides/chase-late-invoices/

From Archon & Partners. Replace everything in [square brackets], read each email, and send it from your own address. Check your contract before mentioning interest or pausing work. This is not legal advice.

=== 1. A week before the due date ===
When: 7 days before due. A phone call works better; use this email if you cannot reach them.
Subject: Invoice [number] for [project], due [due date]

Hi [first name],

A quick check ahead of the due date. Invoice [number] for [project] ([amount]) is due on [due date].

Could you confirm that it has reached the right person, and that you have everything you need to process it (purchase order number, supplier form, approval)? If anything is missing, tell me and I will send it today.

Thank you,
[your name]
[firm name]

=== 2. On the due date ===
When: Day of due date, only if payment has not arrived.
Subject: Invoice [number] is due today

Hi [first name],

Invoice [number] for [project] ([amount]) is due today, [due date]. The payment details are on the invoice, and I have attached a copy.

If payment is already on its way, thank you, and please ignore this note. If you have a question about the invoice, call me on [your number] and we will sort it out.

[your name]
[firm name]

=== 3. Seven days late ===
When: 7 days after the due date. Follow the email with a call the same week.
Subject: Invoice [number], 7 days past due

Hi [first name],

Invoice [number] for [project] ([amount]) was due on [due date], and we have not yet received payment. Could you tell me where it stands in your approval process, and when we can expect payment?

I have attached the invoice again. If something is holding it up, such as a missing document or a question about the amount, tell me and I will resolve it this week.

[your name]
[firm name]

=== 4. Fourteen days late ===
When: 14 days after the due date. Send it, then phone.
Subject: Invoice [number], 14 days past due: payment date needed

Hi [first name],

Invoice [number] for [project] ([amount]) is now 14 days past its due date of [due date]. I would like to agree a payment date with you. Could you reply with the date by [reply-by date]?

Our agreement ([section reference]) sets payment at [payment terms]. I would like to keep the project moving, so I will call you on [day] to agree the date.

[your name]
[firm name]

=== 5. After a phone call ===
When: The same day as any call about the invoice, so the agreement is on record.
Subject: Following our call: invoice [number]

Hi [first name],

Thank you for the call today. To confirm what we agreed:

- Invoice [number] for [amount] will be paid on [date] by [payment method].
- [Open question: who will answer it, and by when.]

If I have anything wrong, please tell me. I will check on [date].

[your name]
[firm name]