[DATE, ex. Wednesday, June 11, 1998]

[NAME, COMPANY AND ADDRESS, ex.
John Smith
XYZ Inc.
1234 First Street
Suite 567
Anycity, Anystate  85245]
 

Dear [NAME, ex. John Smith], 

Since we value your business greatly, I have been inspecting our invoices to ensure that we have made no errors.

You can understand, then, my embarrassment when I uncovered an error on our invoice #[ INVOICE NUMBER]. [STATE ERROR, ex. Although we shipped to you five Magnaflux compressors, per your order, we incorrectly billed you for four compressors.]  Please check your records and notify me if I am mistaken. 

I will nullify that invoice ( #[INVOICE NUMBER, ex. #A423F] ) and issue you a new one as follows:

[LIST NEW INVOICE DETAILS, ex.

          5 Magnaflux compressors @ $4,000                   $20,000
          Tax @ 5%                                                       1,000
          Total                                                              $21,000]

Let me assure you that I will personally inspect our invoices to you in the future to ensure that there will be no further errors.  Feel free to contact me at XXX-XXXX if there are any issues you wish me to address. 

Sincerely,

[YOUR NAME, ex. Jill Jones]