A late invoice is awkward for both sides. The client knows it is late, and you know they know. The trick is to make paying easier than ignoring you.
1. Send the reminder before it is late
Three days before the due date, send a short note with the invoice attached and a link to pay. Most late payments are forgotten ones.
2. Keep the first chase friendly
On the day it is due, assume good faith. Ask whether they need anything from you to process it.
- Resend the invoice, never just the amount
- Name the project, not the money
- Give one way to pay, not four
Nobody has ever paid faster because the reminder was angrier.
3. Put the late fee in writing first
A fee only works if the contract said so before the work started. Mention it once, calmly, in the second reminder.