Invoice disputes and collections between AP and AR agents

How it works today

An invoice reaches the buyer as an X12 810 Invoice, a cXML InvoiceDetailRequest, a Peppol BIS Billing document, a supplier portal upload, or a PDF by email. Accounts payable matches it against the purchase order and the goods receipt. When the lines disagree, the work turns manual. An AP clerk emails the supplier, the supplier’s accounts receivable team checks the order, and the fix comes back as a credit note, a corrected invoice or a short payment with an explanation. X12 has sets for each piece: an 812 Credit/Debit Adjustment, an 820 Payment Order/Remittance Advice, and an 824 Application Advice to report the result of processing a received document. Collections run the other way: an AR collector chases overdue invoices by email and phone.

Peppol gives disputes a vocabulary. The Peppol BIS Invoice Response 3.2, a UBL ApplicationResponse, lets the buyer tell the seller exactly where an invoice stands:

Code	Name	Meaning in Peppol BIS
AB	Message acknowledgement	Received and readable (buyers must support)
IP	In process	Processing has started
UQ	Under query	Buyer will not proceed without more information
CA	Conditionally accepted	Accepted on stated conditions, to be paid accordingly unless the seller disputes
RE	Rejected	Buyer will not process this invoice further (final; buyers must support)
AP	Accepted	Final approval; next step is payment (buyers must support)
PD	Paid	Payment initiated (final); with reason PPD, partially paid

Two code lists explain the status. The reason list (OPStatusReason) includes REF (references incorrect), LEG (legal information incorrect), DEL (delivery issues), PRI (prices incorrect), QTY (quantity incorrect), ITM (items incorrect) and PAY (payment terms incorrect). The action list (OPStatusAction) tells the seller what to do: PIN (provide information), NIN (issue a new invoice), CNF (credit fully), CNP (credit partially) or CNA (credit the amount).

North America has no Peppol Authority. As of 26 September 2026, OpenPeppol’s list of Peppol Authorities includes neither the United States nor Canada. US B2B e-invoicing is industry-led. Participants in the Business Payments Coalition’s E-invoice Exchange Market Pilot formed the Digital Business Networks Alliance (DBNAlliance) in 2023 as the legal entity overseeing a new exchange network. It uses a four-corner model: supplier, two access points and buyer. DBNAlliance says it has launched this open exchange network for US companies. For Canada, we found no national B2B e-invoicing framework or mandate as of the same date, so Canadian companies rely on EDI, supplier portals and email.

Fraud rides on invoices. The FBI’s business email compromise guidance gives the example of a regular vendor sending an invoice with an updated address, and advises verifying any change in account number or payment procedure with the requester directly.

The agent-to-agent version

Illustrative. A buyer’s AP agent puts an invoice under query with the supplier’s AR agent, carrying Peppol codes as structured data in A2A v1.0 shapes:

{
  "jsonrpc": "2.0",
  "id": "inv-disp-4410",
  "method": "SendMessage",
  "params": {
    "message": {
      "messageId": "msg-inv-4410-01",
      "role": "ROLE_USER",
      "parts": [
        { "text": "Invoice INV-88213 is under query. Line 2 is billed at 14.20 per unit, but PO 45-7731 agreed 13.60. Please issue a partial credit note for the difference." },
        {
          "data": {
            "invoiceNumber": "INV-88213",
            "purchaseOrder": "45-7731",
            "responseCode": "UQ",
            "statusReason": "PRI",
            "requestedAction": "CNP",
            "disputedLines": [
              { "line": 2, "quantity": 400, "invoicedUnitPrice": "14.20", "agreedUnitPrice": "13.60", "currency": "USD" }
            ]
          },
          "mediaType": "application/json"
        }
      ]
    }
  }
}

Then:

1. The supplier’s AR agent checks the order and its price list. If the buyer is right, it issues the credit note and completes the task with the credit note as an artifact. If the price change was agreed later, it replies with the evidence, and the task waits in TASK_STATE_INPUT_REQUIRED.
2. The AP agent marks the rest of the invoice accepted (AP) and schedules payment.
3. Remittance names both the invoice and the credit, whether it travels as an X12 820 or in the payment details.
4. For collections, the AR agent asks for the status of overdue invoices and gets structured answers instead of a voicemail: in process, under query with a reason, or accepted with a payment date.

What has to be true

Identity. Both agents must map to a vendor or customer record each side already holds. A Signed Agent Card proves who holds the key, which helps, but bank details are the highest-risk field. Following the FBI’s advice, a change of payment instructions should never be accepted from the channel alone, however trusted the agent.

Authority. Accepting a credit, agreeing a write-off and promising a payment date are commitments. Each agent needs limits, such as a maximum credit it may accept or grant without a person, and the other side needs to see them.

Record. A dispute trail must show who asked, what was claimed, which code applied and what was agreed. Credit notes need duplicate protection. The A2A specification lets agents use messageId to detect duplicate messages, and a retried request must not produce a second credit.

Law. The US Fair Debt Collection Practices Act defines debt as a consumer’s obligation from a transaction mainly for personal, family or household purposes, so invoices between companies fall outside it. Canadian provincial statutes are broader. Ontario’s Collection and Debt Settlement Services Act defines a collection agency as a person, other than a collector, who obtains or arranges payment of money owing to another person, without limiting that to consumer debts. An AR agent collecting a company’s own invoices is in a different position from a service that collects for many suppliers. This describes the texts; it is not legal advice.

Where Emissar fits

• Front Door (Open to design partners): a hosted A2A endpoint where a supplier’s AR team or a buyer’s AP team exposes invoice status and dispute skills.
• Verify (In development): confirms which company’s agent is asking before anyone shares invoice or payment details.
• Ledger (Spec in progress): a signed receipt of each query, response code and agreed credit that both sides can retrieve.
• Handoff (In development): routes disputes outside an agent’s limits to an AP or AR specialist with the exchange attached.

Open questions

• Will North American networks adopt Peppol’s status and clarification codes, or define their own?
• Should agents carry the Peppol Invoice Response itself as a UBL file part, so existing validation still applies?
• When does an agent that chases payments for many suppliers become a collection agency under provincial law?
• Is a payment date an AP agent gives a commitment, an estimate, or neither, and how should it be labeled?