Subject: An option for settling invoice [#1234]

Hi [CLIENT NAME],

I understand cash flow can get tight. Rather than let invoice [#1234]
([$TOTAL]) sit unresolved, here's what I can offer:

  [3] payments of [$X], due on [DATE 1], [DATE 2], [DATE 3].

If you agree, reply "confirmed" to this email and I'll treat that as
our agreement. If the first payment isn't received by [DATE 1], the
full original balance becomes due immediately.

This offer stands until [DATE — 7 days out].

Regards,
[YOUR NAME]
