SubjectInvoice, due yesterday
Hi [their name], Quick one: my invoice for [amount] was due yesterday. I've attached it again in case it got buried. Thanks, and thanks again for the work. [your name]
Three emails for an overdue invoice, friendly to firm, with your details filled in and the day to send each. Nothing you type leaves your device.
SubjectInvoice, due yesterday
Hi [their name], Quick one: my invoice for [amount] was due yesterday. I've attached it again in case it got buried. Thanks, and thanks again for the work. [your name]
SubjectInvoice, now 14 days overdue
Hi [their name], My invoice for [amount] is now two weeks overdue. It's attached again. When can I expect payment? Thanks, [your name]
SubjectInvoice, final reminder
Hi [their name], My invoice for [amount] is now 30 days overdue. Please pay it by [a date]. If I haven't received it by then, I'll pause any further work until it's settled. [your name]
Most late payers forgot, so the first email assumes they did. The second asks one question, because a question gets an answer. The third names a date and only says what you’ll really do. If none of them work, pick up the phone.
The longer version: how to chase an unpaid invoice. No invoice yet? The free invoice generator makes one.

Flexi sends each one on its day after your yes, and stops the moment they pay.