A weekly bill run with AI checks

Most bad payments to suppliers fall into a few kinds. The same bill gets paid twice because it arrived as an email and again as a paper copy. A price creeps up and nobody compares it to the quote. A bill arrives for work that wasn't done or goods that never turned up. And a supplier's bank details "change" in an email that the supplier never sent. Requests to change payment details are a common route for invoice fraud, and they tend to arrive just before a payment is due.

Paying bills once a week, in one batch, with a fixed set of checks, catches most of these. An AI assistant does the slow part: reading each bill, pulling out the fields, and comparing them to what you've paid before. A person clears every flag, and only a person approves and makes payments. The AI never pays, never approves, and never edits a supplier record.

Plan on 20 to 45 minutes a week once it's set up, depending on how many bills you get.

What you need

• This week's bills, as PDFs or images, in one folder
• Paid bills from the last 90 days, exported from your accounting system: supplier, bill number, bill date, amount, date paid
• Your supplier list, exported with supplier name, usual payment terms, and the last four digits of the bank account you pay (delete the full account and routing numbers before upload)
• Open purchase orders or accepted quotes, if you use them, with supplier, reference, line items and agreed prices
• A chat assistant that reads PDFs and spreadsheets, on a business plan whose data terms your owner has approved for financial records

Pick one day for the run, early enough in the week that a held bill can still be paid on time once it clears.

Settings: fill these in once

Step 1: pull the fields off each bill

Upload the week's bills and use this prompt.

I've attached this week's supplier bills. For each bill, make one row with:
supplier name, bill number, bill date, due date, service period or delivery
date, PO or quote reference, each line item (description, quantity, unit
price, line total), subtotal, tax, total, and payment details as printed on
the bill (last four digits of the account only).

Rules:
- Copy values exactly as printed. If a field is not on the bill, write
  NOT SHOWN. Do not guess or fill in from other bills.
- If a page is hard to read, say which bill and which field.
- At the end, give the number of bills you read and the sum of all totals.

• The bill count matches the number of files in the folder
• Open three bills and check every field in their rows against the PDF
• Add up the bill totals yourself (or in the accounting system's draft batch) and compare to the AI's sum

If any of these fail, fix the problem (often a scanned page or a bill with two invoices in one file) and run Step 1 again before going on.

Step 2: run the checks

In the same chat, upload the paid-bills export, the supplier list and the open POs, and use this prompt.

Using the table you just made, run these checks on every bill and list
every flag. Do not explain why a flag happened.

1. DUPLICATE: same supplier and bill number as any paid bill or any other
   bill this week; or same supplier and same total as a paid bill within
   {duplicate window}.
2. ARITHMETIC: line totals don't equal quantity x unit price; lines don't
   add up to the subtotal; subtotal plus tax doesn't equal the total.
3. PRICE: any unit price more than {threshold} above the matching PO or
   quote line, or above the same item on this supplier's last bill.
4. NO REFERENCE: no PO or quote reference, for suppliers that normally
   have one.
5. NEW SUPPLIER: supplier not on the supplier list.
6. BANK DETAILS: last four digits on the bill differ from the supplier
   list, or the bill or its covering email mentions new bank details.
7. TERMS: due date doesn't match the supplier's usual terms.
8. PERIOD: service period or delivery date is in the future, or more
   than 60 days ago.

Output a table: bill number, supplier, total, check number, what you
found, and the values compared.

• Every bill appears in the output, either with a flag or listed as "no flags"
• Spot-check one flagged and one unflagged bill against the source files

Step 3: clear the flags

Every flag needs a reason backed by a document, or the bill is held. Copy the flags into your bill-run sheet.

What usually clears each flag:

The bank details rule has no exceptions. Don't reply to the email asking to confirm, and don't call a number printed on the new bill. Look up the number in your own records, call it, and ask the supplier to confirm the change. Until that call happens, pay to the old details or hold the bill.

Step 4: approve and pay

• Only cleared bills go into the payment batch
• Bills over the second-approver limit, and every bill from a new supplier, have a second approver's sign-off
• The payment batch total in your bank or accounting system matches the sum of cleared bills
• Held bills have a note saying what's missing and who's chasing it
• Any change to supplier bank details is made in the supplier record by a person, after the call, and noted with the date and who confirmed it

Sign-off

WEEKLY BILL RUN

Run date:                   Bills received:        Total received: $
Flags raised:      Cleared:      Held:      Rejected:
Bills paid:                 Total paid: $
Bank detail changes this week, and how each was confirmed:
1.
2.
Held bills and next step:
1.
2.

Prepared by:                Date:
Approved for payment by:    Date:

Where the business has two people, the person who prepares the run should not be the one who approves payment. In a one-person office, the owner approves on the strength of this sheet.

A worked example

Larchmont Print & Sign, a fictional 14-person shop, runs its bills every Tuesday. One week it had 23 bills. The AI flagged five. Two were the same ink supplier bill, received by email and by post; one was rejected. A vinyl supplier's unit price was 9% above the quote; the quote was found, the supplier sent a corrected bill, and it was paid the following week. A courier bill had no PO, and the production manager confirmed the rush delivery. The fifth was a packaging supplier bill with a new account number and a cover email saying the supplier had changed banks. The office manager called the supplier on the number in the supplier file. The supplier hadn't changed banks, the email was fake, and the bill was paid to the original account.

Keep it running

Keep each week's sign-off and flag table together in one folder. Once a quarter, look at which flags clear the same way every week and tighten or loosen the thresholds so the list stays short enough that someone reads every row. Never relax the bank details or duplicate checks.

Do it with Merit AC: the AI Skills Academy course walks through prompt writing and output checking for business tasks one lesson at a time.