What is the Peppol Message Level Response (MLR)?

In this article, we take a look at the current discussions within the international Peppol organization as well as KOSIT in Germany regarding the mandatory introduction of the Peppol Message Level Response.

The Peppol-supported message responses are the technical features at stake. These include: Transport Acknowledgements (Ack), Message Level Responses (MLRs), and Business Level Responses (or Invoice Responses).

Frequently Asked Questions about Peppol Message Level Response and Invoice Response

Peppol supports three basic message types, each serving different functions:

1. Transport Acknowledgement (Ack)
   ACKs are almost always sent by invoice recipients and inform the sender of the invoice about whether their document/invoice was successfully transmitted or not. Peppol and Invoice Portal automatically process these for the user.
2. Peppol Message Level Response (Peppol MLR)
   MLRs inform the sender of the invoice about whether their invoice is correctly structured or not. The correct structure is based on the agreed specifications (between the sender and the recipient of the invoice). MLRs are frequently sent, although the German portals ZRE and OZG-RE are not yet processing them. However, both ZRE and OZG-RE plan to process MLRs in 2024!
3. Invoice Response / Business Level Response (BLR)
   These inform the sender of the invoice about the status of their sent invoice. Status types include:

• Accepted
• Rejected
• Validated
• Paid
  BLRs are rarely sent by invoice recipients. Peppol is programmed to process them, but administrations usually contact the invoice senders directly when there is an issue.

Each of the three Peppol message responses follows specific standards. This ensures the security and integrity of the data of Peppol users.
Peppol always applies up-to-date standards and protocols to handle user data responsibly and reliably. This also applies to Peppol message responses.
To fully understand how these message responses work, it’s useful to refresh your understanding of the Peppol billing process. Specifically, it’s helpful to revisit your understanding of the “Four-Corner Model” of PEPPOL.

Message Sequence Diagram
Peppol processes sensitive and often important data. Therefore, it is crucial that Peppol users feel secure in this process.
Peppol supports message responses for each step of data exchange. These message feedbacks help confirm the responsible handling of user data by Peppol.
Message responses are generated and transmitted at different times and for different purposes. The following diagram provides an overview of these time points and purposes:

• Ack messages are sent after the document is transmitted. The Ack transports the information between the sender’s access point and the recipient’s access point.
• MLR messages are sent after the invoice/document has been sent. However, they are sent before the document is received by the recipient. The MLR messages are transmitted between the sender’s and the recipient’s messaging systems, usually the respective Peppol access points; sometimes they are also integrated into ERP/CRM/EDI systems.
• BLR messages are typically transmitted between the sender’s and recipient’s access points (or sometimes their ERP/CRM/EDI systems). They are sent at different times, depending on the progress of the invoice processing.

Peppol’s Message Responses
Below are explanations of the functional and technical characteristics of message responses.

1. Ack (Transport Acknowledgement) (Corner 3 to Corner 2)
   What is an ‘Ack’?
   An Ack is an automated message response to the sender of a message/document/invoice. Peppol supports the sending of these message types, and Invoice Portal processes them for its users.
   What does an ‘Ack’ do?
   An Ack informs the invoice sender whether their invoice has been successfully delivered (or not).
   If the invoice has been successfully sent, the invoice sender will receive an Ack to inform them. If the invoice couldn’t be sent, the invoice sender will receive an Ack to inform them.
   This is similar to receiving an automatic email confirmation when shopping online. When you order one or more products for delivery, you receive an email confirming your order.
   But there is a crucial difference between an email confirmation when shopping online and an Ack. The difference is that the information conveyed by Acks requires additional security. And Peppol ensures this security.
   It’s also worth noting what Acks do not do: If your invoice is formatted incorrectly, the Ack will not inform you.

How is an ‘Ack’ sent?
Peppol Ack messages are sent using the AS4 messaging standard.
What is AS4? AS4 is a widely used and trusted standard for B2B and B2G e-messaging. The use of AS4 by Peppol is further proof of Peppol’s up-to-date technology. AS4 refers to an Ack as a SignalMessage.
There are three types of SignalMessage:

• SignalMessage/Receipt
• SignalMessage/Error
• SignalMessage/PullRequest (not used in Peppol)

A SignalMessage automatically responds to the success (or failure) of a data transmission. This success or failure is tracked by Peppol.
But an Ack is not just a regular confirmation message…
Acks that conform to the AS4 protocol protect and secure users’ data. They assure senders and recipients that their documents are processed without problems.
No one can simply claim they sent documents or say that no documents were received. Acks ensure efficiency in Peppol’s digital B2B and B2G messaging processes.

How does an ‘Ack’ work?

1. The sender sends their document. The document is then automatically assigned a unique ID by Peppol and the Invoice Portal.
2. A SignalMessage/Receipt is automatically sent to the sender when the document has been successfully sent.
3. Or a SignalMessage/Error is automatically sent to the sender if the document could not be successfully sent.

And that’s it! This simplicity is the beauty of Peppol’s Acks. Furthermore, the security and up-to-date AS4 technology guarantees the quality of service.