A reminder is one of the few messages a client reads closely from beginning to end. It concerns money they owe, so attention is guaranteed. That makes it an unusually expensive place to sound careless.
Lead with the fact, not the feeling
Open with the invoice, the amount and the date. Do not open with an apology for chasing, and do not open with a complaint. Both make the message about you rather than about an unpaid invoice.
The best first line is boring and specific: which invoice, how much, when it was due. The reader knows immediately why the message exists, and nothing in it can be read as an accusation.
Ask a question you actually want answered
"Please remit payment at your earliest convenience" invites no reply, so you learn nothing. "Is anything holding this up on your side?" invites one, and a reply is worth more than a payment promise, because it tells you which problem you are solving.
A reminder that produces a reply has done its job, even when no money moves that week.
Name the context if you know it
If the payer changed controllers, mention it. If there was a handover, a holiday period, or a disputed line on a previous invoice, mention that. Demonstrating that you know the account converts a generic chase into a conversation, and it makes the eventual escalation credible rather than mechanical.
Four openings that work
- A plain status check: the invoice, the amount, the due date, and one question.
- A reference to a specific prior exchange: a call, a promised payment run, a named contact.
- An offer that removes friction: re-send the PDF, split across two dates, confirm the PO reference.
- A short note before the due date confirming the invoice arrived at the right desk.
Three that reliably cost you
- Passive aggression dressed as politeness. "As you are no doubt aware" is read exactly as intended.
- Threats you have not decided to carry out. An escalation you do not follow through teaches the payer to ignore the next one.
- Automated tone with a human signature. If it is signed by a person, it should read as though a person could have written it.
Where the amount belongs
In the body, once, in a form the reader can act on: the figure, the invoice number, and the original due date together. Not in the subject line, where it looks like a dunning notice, and not repeated three times, which reads as pressure.
Sign it with a person
Send from a named individual at a monitored address. A reply that reaches nobody is worse than no reply, because the payer believes they have answered and you believe they have gone quiet.