What’s a request for payment that’s over a month late and sounds like a bell?

Dun. Ever since I returned to working for myself in 2000, I have included on my invoices a notice at the bottom:

Terms: Net 30, 1.5% per month (18% per annum)

What this means is that payment is due in full within 30 days of the date of the invoice, and late payments are subject to a fee of 1.5% of the past due amount
per month or 18% per year…which, when you get down to it, really is not that bad, considering some rates on credit cards and the fact that I am not really in
the money lending business. I had never had to use this clause until this past month, when one of my most frequent customers neglected to pay their bill for
work I had done in August. I had intended to post their name if the check hadn’t arrived today, but it did, so they are apparently getting things under control.
Still, I think I may need to review my rate…I may be limited by statute.