[Your letterhead, if desired; if not, your return address]
[Date of letter—month, day, and year]
[Recipient's first and last names]
[Street or P.O. box address]
[City, State ZIP code]
Dear [recipient's name]:
Thank you for the note you sent to follow up on the payment that our company owes to your business. I am writing to apologize for this payment being late in arriving to you. Per our records, the invoice number is 89766, and the amount for this is $759. We will mail the check for this invoice on Monday, August 15.
Thank you for your patience, and again, I apologize for the payment delay and for any inconvenience it might cause. We appreciate the business relationship that we have built with you and look forward to continuing to work together.
[Sender's first and last names]