A bank letter is an official document from your bank that provides important information about your business' official bank account. You must complete, sign and date the form.Please also be aware that the same bank account must be used for any contracting entities associated with an NPI. Simply complete and. How can I be sure my bill has been paid? Instructions for completing this form are on the back. Simply complete and. How can I be sure my bill has been paid? Instructions for Completing the Form. Determine which bank accounts will be used for direct deposit.