Peppol Invoice Response vs MLR and MLS explained

Peppol has two kinds of "reply" to an invoice, and they answer different questions. A Message Level Response (MLR), or its successor Message Level Status (MLS), is a technical message between service providers: was the invoice valid and delivered? An Invoice Response is a business message from buyer to supplier: what is happening with this invoice: queried, rejected, approved, paid? Both use the same codes, AB, AP and RE, but with different meanings, which causes a lot of confusion.

The three layers of response

The MLS specification describes three groups of status messages:

Layer	Example	Peppol message
Transport	"Your Access Point received the bytes"	AS4 receipt (automatic)
Message	"The invoice failed validation" or "it was delivered to the buyer"	MLR (old) / MLS (new)
Business	"We dispute line 3" or "Approved for payment"	Invoice Response

MLR: Message Level Response

Peppol BIS Message Level Response 3.0 lets the receiver of a document tell the sender whether it passed validation.

• Codes: AP (accepted, no fatal errors), AB (acknowledged, not validated), RE (rejected, with a description of the errors)
• Identifiers: CustomizationID urn:fdc:peppol.eu:poacc:trns:mlr:3, ProfileID urn:fdc:peppol.eu:poacc:bis:mlr:3
• An MLR is sent only if the sender asked for one, or if fatal errors were found.

MLS: Message Level Status (the replacement)

Peppol Message Level Status v1.1.0 (2 July 2026) is "an evolution based on Message Level Response (MLR)". It is sent by the buyer's provider (C3) to the supplier's provider (C2). It reports on validation and also on whether the invoice was passed on to the buyer (C4).

MLS code	Meaning	Status reason codes
RE	Rejected or not delivered. "The responsibility of the message is transferred back to C1/C2."	SV schema error; BV business rule or other violation (including file size, malware, MIME mismatch); BW warnings (reported only alongside fatal errors); FD delivery to C4 failed
AP	Delivered towards C4 with confirmation, for example by API with an acceptance acknowledgement	optional
AB	Delivered towards C4 without confirmation, for example by email or postal service	optional

What is mandatory for providers (Peppol Network Policy v1.0.0, 2 July 2026):

• MLS-1: every service provider "MUST support sending and receiving MLS messages".
• MLS-2: providers must register to receive MLS under their OpenPeppol Service Provider ID, scheme 0242 (for example 0242:987654).
• MLS-3: negative MLS is always sent. Positive MLS is sent only if the sending provider opts in. The default is FAILURE_ONLY, and ALWAYS_SEND is the alternative.
• MLS-4: no artificial delays. Service levels require 99.5% of MLS messages (for documents under 10 MB) to be sent within 20 minutes of the original transmission, measured monthly.

During the transition, providers may run MLR and MLS in parallel. Each document gets only one or the other, and MLS takes priority where both are supported. OpenPeppol says MLR "is being phased out".

The MLS document type ID is:

urn:oasis:names:specification:ubl:schema:xsd:ApplicationResponse-2::ApplicationResponse##urn:peppol:edec:mls:1.0::2.1

What it means for you: if your invoice is rejected by the buyer's provider, your provider should learn about it within minutes, with a reason code. Ask how that reaches you (see How to choose a Peppol Access Point).

Invoice Response: the business conversation

BIS Invoice Response 3.2 lets the buyer report the status of an invoice to the seller. The BIS states that responses "have no legal effect". They do not change the invoice or anyone's commercial obligations.

Code	Name	Meaning	Final?
AB	Message acknowledged	Buyer has a readable invoice it can process	No
IP	In process	Processing has started	No
UQ	Under query	Processing halted until the seller answers a query	No
CA	Conditionally accepted	Accepted on stated conditions	No
RE	Rejected	Buyer will not process it further	Yes
AP	Accepted	Final approval; payment is the next step	No
PD	Paid	Payment initiated for the full amount	Yes

Statuses follow that order, though not every step has to be sent. A buyer supporting the BIS must at least handle AB, RE and AP. UQ and RE require a clarification, using reason and action code lists (OPStatusReason, OPStatusAction).

Identifiers: CustomizationID urn:fdc:peppol.eu:poacc:trns:invoice_response:3, ProfileID urn:fdc:peppol.eu:poacc:bis:invoice_response:3.

New in 2026: "billing with response"

The May 2026 release of Peppol BIS Billing 3.0 (3.0.21, mandatory from 17 August 2026) added an optional profile, urn:peppol:bis:billing_with_response, "for a process where an invoice response is required step in the collaboration". It needs a separate SMP registration, and the same profile ID was added to the Invoice Response BIS. A buyer that registers for it is signalling that it will always reply.

Worked example

A supplier in Leeds sends an invoice to a buyer in Bristol (both fictional):

1. 09:00 The supplier's provider validates and sends the invoice.
2. 09:04 The buyer's provider finds a fatal business-rule error and sends MLS RE, reason BV. The invoice never reaches the buyer, and the supplier must fix it and resend.
3. 10:15 The corrected invoice is sent. Since the supplier's provider asked for ALWAYS_SEND, an MLS AP follows: delivered into the buyer's ERP with confirmation.
4. Next day The buyer sends Invoice Response UQ: "PO number missing".
5. The supplier answers outside Peppol, or issues a credit note and a new invoice.
6. Week 3 The buyer sends Invoice Response AP, then PD when payment is initiated.

What is not settled for the UK

Confirmed: Peppol will be the core network for UK e-invoicing from April 2029. MLS is now a Peppol-wide requirement for service providers.

Not yet confirmed (as of 20 October 2026): whether UK rules will require buyers to send Invoice Responses (for example to support late-payment policy), whether rejection has any VAT consequence, and what happens to an invoice that is technically rejected near a VAT period end. Watch the roadmap at Budget 2026.

What to do now

1. Ask your provider whether it supports MLS today and how rejections are shown to you.
2. If you are a buyer, consider sending at least AB, RE and AP. It saves suppliers chasing you.
3. If you are a supplier, check whether your software can receive Invoice Responses and show them against each invoice.
4. Related: Common Peppol validation errors and Credit notes in Peppol.