Subject: Invoice [#1234] from [YOUR BUSINESS] — due [DATE]

Hi [CLIENT NAME],

Thanks again for the opportunity to work on [PROJECT]. Attached is
invoice [#1234] for [$AMOUNT], due [DATE] ([NET TERMS] days).

Payment details are on the invoice. If anything looks off or you need
it formatted differently for your accounts team, just reply and I'll
sort it out same day.

Best,
[YOUR NAME]
