For a rush job, I’d be direct but still factual. The useful move is to stop making it about frustration and make it about the unresolved business item.
Example:
“Hi [Name], following up on the $400 rush job invoice sent with the live site link on [date]. Payment is still outstanding. Could you confirm payment status today, or let me know if there’s an issue preventing payment?”
If there’s no response after that, I’d move to a firmer written notice with the invoice attached again and a specific follow-up date. The main thing is to stop sending open-ended reminders.