The Corner Model, Explained
Two, three, four, five corners: the language of e-invoicing describes who stands between a supplier and a buyer when an invoice travels. This article explains each model with a flow chart and real examples, shows where countries sit, follows one group’s invoices through five routes, and draws the consequences for SAP.
A companion to E-invoicing, Explained from the Ground Up: that article covers the four control models; this one goes into who carries the invoice.
Concepts · Status at 13 October 2026 · Finance, tax and IT teams · Level: foundations, no prior knowledge
2 · 3 · 4 · 5
the corner models, from a direct link to the tax authority joining the exchange
3
questions that place any regime in its model
€1,000
the same invoice, followed through five routes in one group
1 cockpit
one framework and one cockpit for every route
A Simple Question with Large Consequences
Every e-invoice starts with a supplier and ends with a buyer; those are always two corners. The question the corner model answers is: who else is in the middle, and what do they do? The answer decides how many connections you build, who you depend on, and who sees your invoices.
Direct: supplier and buyer connect to each other
One shared hub in the middle
Each side has its own provider; providers interconnect
The four corners, plus the tax authority receiving data
An analogy: telephones
In the early days, a telephone line connected two specific places: a two-corner world. Then exchanges appeared, but you could only call people on the same exchange: three corners. Today you choose your own mobile operator and can call anyone, because operators interconnect: four corners. In some countries the regulator also receives a record of every call. That is the fifth corner.
The Vocabulary
| Term | Meaning |
|---|---|
| Corner | A party or system an invoice passes through on its way from supplier to buyer |
| Access point / provider | A service that sends and receives invoices on a company’s behalf, often certified |
| Network | A set of providers that agree to interconnect under common rules; Peppol is the best known |
| Directory | The network’s address book: who can receive, through which provider, in which formats |
| Participant identifier | A company’s address on the network: a scheme code plus a number, such as a VAT or company number |
| Clearance | A model in which the state platform must validate an invoice before it is valid: a central hub rather than a corner |
Corners describe the route, not the format
The corner model says who carries the invoice. The format (UBL, CII, a national XML) is a separate question, and so is the legal effect. A four-corner network can carry any agreed format; a country can make the network compulsory or leave it optional.
Three questions that place any regime
- Can supplier and buyer use different providers and still reach each other? If yes, it is at least four corners.
- Does the authority receive data from the exchange? If yes, there is a fifth corner.
- Must the authority accept the invoice before it is valid? If yes, it is clearance: the state is the hub.
What the corner model does not tell you
It does not say which format is required, when an invoice becomes legally valid, or what happens on rejection. Two four-corner countries can have very different rules on all three. Always read the corner model together with the country’s legal rules.
Direct Exchange
In the two-corner model, the supplier’s system talks directly to the buyer’s system. Format, channel and security are agreed one to one, often in an EDI agreement.
Two corners: one connection per trading partner
Every new trading partner = a new connection, a new mapping, a new test
Examples
| Example | How it works |
|---|---|
| EDI with a large retailer | EDIFACT or similar messages over a direct secure connection, set up for that customer |
| ERP-to-ERP connection | Two companies, often within a group, connect their systems by API |
| Structured file by email | A supplier emails an XML invoice the buyer’s system can read: direct, but rarely secure or tracked |
Strengths
- No intermediary, no per-invoice fees
- Full control over format and timing
- Efficient for a few very large partners
Limits
- Every partner is a new project
- Does not scale to hundreds of customers or suppliers
- On its own, does not meet mandates that require a certified provider or a copy to the state
Where two corners still matter
Many companies keep EDI with their largest customers. Under a mandate, those flows usually have to be re-routed or copied through the network or platform the law requires: a frequent and underestimated piece of work.
Example: EDI with a retailer, step by step
- AgreeMessage standard, identifiers, transport and test plan, in an interchange agreement.
- BuildMap the SAP billing document to the retailer’s message; set up the connection.
- RunInvoices sent per delivery; acknowledgements returned; errors handled partner by partner.
The Cost Profile
| Cost | Two corners |
|---|---|
| Per invoice | Close to zero |
| Per new partner | High: a project each time |
A Shared Hub
In the three-corner model, supplier and buyer both connect to the same hub: a service provider, a buyer’s supplier portal, or a marketplace. Each side has one connection, but only to partners on that hub.
Three corners: a shared hub
Simple, as long as both parties use the same hub
Examples
| Example | How it works |
|---|---|
| Buyer’s supplier portal | A large buyer asks every supplier to submit invoices through its procurement network |
| One provider for both | Supplier and buyer happen to use the same e-invoicing provider |
| Marketplace billing | Platforms that invoice on behalf of sellers to buyers inside the platform |
Clearance countries put a state platform in the middle. It is a hub in the three-corner sense, but with legal power: the invoice is valid only once the platform accepts it.
When the hub is the state
The invoice exists only once the platform accepts it, for example in Italy (SdI) or Poland (KSeF)
State Hubs: Examples
| Country | State hub | Since |
|---|---|---|
| Italy | Sistema di Interscambio (SdI): every domestic B2B invoice | 2019 |
| Poland | KSeF: the invoice exists once it has a KSeF number | 2026 |
| Serbia | SEF: state platform for B2B and B2G | 2023 |
| Latin America | Clearance through the authority or authorised providers: Mexico, Chile, Brazil | 2000s |
Commercial hub
- Chosen by the parties
- Lock-in: partners on other hubs are hard to reach
State hub
- Imposed by law; everyone connects
- The platform’s availability becomes your billing availability
A provider in front of the hub
Many companies reach a state hub through a service provider. On paper that adds a corner; in practice the state platform still decides validity, and the provider is a channel. Count the corners by who has authority over the invoice, not by the number of systems it passes.
The Peppol Network
In the four-corner model, supplier and buyer each choose their own access point, and access points interconnect under common rules. Before sending, the supplier’s access point looks the buyer up in the network directory to find its access point and the formats it accepts.
Four corners: choose your provider, reach everyone
Before sending, the supplier’s access point looks the buyer up in the directory.
One Invoice, Step by Step
- CreateSupplier ERP creates the invoice and hands it to its access point
- Look upAccess point finds the buyer in the directory: endpoint and formats
- ValidateAccess point checks the invoice against the network specification
- TransmitSecure exchange to the buyer’s access point (AS4)
- DeliverBuyer access point delivers to the buyer’s ERP and confirms
A participant identifier, decoded
Other schemes use VAT or company registration numbers. The identifier is what the directory looks up. Example number fictitious.
The Building Blocks of Peppol
| Component | Role |
|---|---|
| OpenPeppol | The association that governs the network; national Peppol Authorities run it locally |
| Access points | Certified providers that send and receive: corners 2 and 3 |
| Directory (SML and SMP) | The central locator and each provider’s capability register |
| AS4 | The secure transport protocol between access points |
| BIS and PINT | Document specifications: Peppol BIS Billing in Europe; international variants such as JP PINT, PINT A-NZ, PINT SG and PINT AE |
Four Corners in Practice: Where the Network Is Used
| Country | How four corners are used | Status |
|---|---|---|
| Belgium | Domestic B2B invoices over Peppol, by law | Mandatory since Jan 2026 |
| Germany | Peppol one of several allowed channels; must be able to receive e-invoices | Receiving since 2025 |
| Nordic countries | Public-sector invoicing over Peppol, widely used in B2B | Long established |
| Australia, New Zealand | PINT A-NZ; government adoption, voluntary for business | Voluntary B2B |
| Japan | JP PINT for qualified invoices; no mandate | Voluntary |
| EU public sector | Many contracting authorities receive over Peppol | Directive 2014/55/EU |
Why the Four-Corner Model Spreads
- Connect once, reach everyone on the network
- Free choice of provider, and freedom to change it
- Common specifications, so data arrives the same way from every supplier
- Governance: certified providers, agreed security and service levels
- Ready for reporting: adding a fifth corner is a natural extension
- Global: the same network across Europe, Asia-Pacific and the Gulf
What a Company Must Manage
| Item | Why it matters |
|---|---|
| Its own participant identifier | Registered in the directory, so customers’ providers can find it |
| Customers’ identifiers | Stored in master data, or looked up, to address each invoice |
| Document types it can receive | Published per participant: invoices, credit notes, orders |
| The provider contract | Service levels, archive, status messages and the exit route |
Four corners do not mean four companies
Corners are roles. A large company can run its own access point and be corners 1 and 2 at once; a provider can serve both supplier and buyer. What makes it four-corner is that the two sides could use different providers, and still reach each other.
Choosing an Access Point
- Is it certified in every country where you need it, including any fifth-corner role?
- Does it integrate with SAP DRC as standard, returning statuses to the SAP document?
- How does it handle inbound invoices, archiving and the exit to another provider?
The Authority Joins
The five-corner model keeps the four-corner exchange and adds the tax authority as a fifth corner. The access points, or approved platforms, send tax data from each invoice to the authority. The invoice travels between companies; the authority sees the data without sitting in the middle.
Five corners: invoices between companies, data to the state
The invoice travels between companies; the authority sees the data without sitting in the middle.
Five-Corner Examples
| Country | How the fifth corner works | Status |
|---|---|---|
| France | Approved platforms exchange invoices and transmit data to the tax administration; e-reporting for B2C and cross-border | Live since Sep 2026; SMEs Sep 2027 |
| Singapore | InvoiceNow (Peppol) with GST invoice data sent to the tax authority | New voluntary registrants 2025–26; all by Apr 2031 |
| United Arab Emirates | Accredited service providers on Peppol (PINT AE), tax data to the Federal Tax Authority | Businesses at or above AED 50M, from Jan 2027 |
| Belgium | Near-real-time e-reporting planned on top of Peppol | Planned 2028 |
Variations on the Theme
| Country | Model |
|---|---|
| Spain | Private platforms or a public solution, with a “true copy” of every invoice sent to the public solution, from October 2027 |
| Croatia | Exchange through intermediaries, with invoice data fiscalised by both sides, and payments reported |
Five corners versus clearance
In clearance, the state sits between supplier and buyer and must accept the invoice first. In five corners, it sits beside the exchange and receives data. The difference shows when the state platform is down: in clearance, invoicing stops; in five corners, invoices still flow.
The Models Side by Side
What changes from one model to the next, and how to tell which one applies.
The Five Models, Side by Side
| 2 corners | 3 corners | Clearance hub | 4 corners | 5 corners | |
|---|---|---|---|---|---|
| In the middle | Nobody | One shared hub | State platform | Two providers | Two providers + state |
| Reach | One partner | Hub members | Everyone, by law | The whole network | The whole network |
| Authority sees | At audit | At audit | Every invoice, first | At audit | Every invoice’s data |
| Valid when | Sent | Sent | Accepted by the state | Delivered | Delivered and reported |
| Main risk | Scale | Lock-in | Platform outage | Directory and data | Consistency of data |
| Examples | EDI | Supplier portals | Italy, Poland | Belgium | France, UAE |
Swipe to see the whole table →
Which model applies? A decision flow
Countries by Model
| Model | Examples (October 2026) |
|---|---|
| Clearance hub | Italy, Poland, Serbia, Romania, Türkiye, Saudi Arabia, Mexico, Chile, Brazil, India (registration) |
| Four corners | Belgium (mandatory), Germany (allowed), Nordic countries, Australia, New Zealand, Japan |
| Five corners | France, Singapore (GST InvoiceNow), United Arab Emirates (2027), Belgium e-reporting (2028) |
| Mixed or own model | Spain (platforms plus public solution), Croatia (intermediaries plus fiscalisation), Greece (licensed providers plus myDATA) |
Where the Trend Is Going
- Networks are converging. More countries adopt Peppol-style interoperability, even with their own formats.
- Reporting is added on top. Four-corner countries add a fifth corner rather than replace the network.
- Europe aligns by 2030. Under ViDA, intra-EU invoices move to digital reporting from 1 July 2030, closer to five corners than to clearance.
The Same €1,000 Invoice, Five Routes
An illustrative manufacturing group sells the same €1,000 spare part from five subsidiaries, each to a local business customer. The commercial content is identical. The routes are not.
Five Journeys of the Same Invoice
| Entity | Model | Journey of the invoice | Valid when |
|---|---|---|---|
| Belgium | 4 corners | SAP → group access point → customer’s access point → customer’s ERP | Delivered over Peppol |
| France | 5 corners | SAP → approved platform → customer’s platform → customer; data to the tax administration | Exchanged through approved platforms |
| Italy | Clearance hub | SAP → SdI, which validates and delivers → customer | Accepted by the SdI |
| Spain | Mixed, from 2027 | SAP → platform → customer, with a true copy to the public solution; or SAP → public solution → customer | Issued through approved channels |
| Germany, to a retailer | 2 corners | SAP → retailer by EDI, as agreed, in a structured format the law accepts | Issued in a valid format |
Swipe to see the whole table →
Simplified. Dates and conditions are in our country briefings; Spain’s B2B obligations start 6 October 2027 for companies above €8 million.
Five routes, one cockpit
Five routes, five status models: one place to see them
What the Group’s Finance Team Sees
- Five statuses with different meanings: delivered, accepted, cleared, copied, sent
- Five places where an invoice can fail, and five kinds of error
- Different deadlines to fix a rejection
- Different identifiers to keep on each document: network IDs, clearance numbers
- Different archives: the provider’s, the state’s, or only its own
- One customer master, five addressing rules
The lesson
A group never lives in one corner model. The design goal is one framework and one cockpit for all routes, so that the meaning of “sent”, “delivered” and “accepted” is clear for every country, and nobody has to log into five portals to know whether last month’s invoices arrived.
What It Means for SAP
One framework, many routes. SAP Document and Reporting Compliance turns billing and purchasing documents into electronic documents and routes each one according to its country’s model: to a network access point, to an approved platform, or to a state platform. SAP also offers Peppol connectivity through its own exchange service, and integrates with third-party access points and providers.
Outbound: from the SAP document to the customer and the authority
What SAP Needs in Each Model
| Model | What SAP needs | Typical decision |
|---|---|---|
| 2 corners | An outbound channel per partner; EDI mapping | Keep, or move to the network |
| Clearance hub | The national format; the state’s identifier and status returned | Direct connection or provider |
| 4 corners | Participant identifiers; a Peppol access point; inbound import | SAP’s Peppol service or a third party |
| 5 corners | As four corners, plus reporting statuses and data consistency | Provider certified in the country |
Master Data the Networks Depend On
- Participant identifiers for customers and for your own companies
- Tax and company numbers, validated
- Accepted document types, from the directory or the customer
- Routing rules by company code, country and customer
Four Design Questions
- One access point for the group, or one per country? Fewer providers, fewer contracts and portals.
- Who owns the directory entries? Your own registration, and customers’ identifiers in SAP.
- How do statuses come back? Every route must return its status to the SAP document.
- What happens to inbound? Received invoices arrive through the same corners, so plan the AP side too.
The receiving side is a corner too
Every model works in both directions. A company that connects SAP for sending but leaves supplier invoices arriving in a provider’s portal has half a solution and, in five-corner countries, a reporting obligation on purchases it cannot see.
Implementation Checklist
- Route map: entity × country × model × provider
- Own participant IDs registered in each network
- Customer and supplier IDs in the business partner
- Status model per route, mapped to the eDocument
- Inbound import and approval in accounts payable
- Provider exit route and archive agreed
Glossary and How We Help
The words you will hear most, five ideas to keep, and what we do with them in SAP.
The Words You Will Hear Most
| Term | Meaning |
|---|---|
| Access point | A certified provider connecting a company to a network |
| Approved platform | A provider authorised by a tax authority to exchange invoices and transmit data |
| AS4 | Secure messaging protocol used between Peppol access points |
| Clearance | Validation by a state platform before an invoice is valid |
| Directory | The network’s address book of participants and capabilities |
| E-reporting | Sending transaction data to the authority, without the invoice itself |
| Participant ID | A company’s address on the network: scheme plus number |
| Peppol | An international network and specifications for e-document exchange |
| PINT | Peppol International Invoice model, with country variants |
| True copy | A copy of the invoice sent to the authority’s platform by the provider |
Five Things to Remember
- Corners describe who carries the invoice, not its format or legal effect.
- Two and three corners are efficient but do not scale or interconnect.
- Four corners let every company choose its provider and still reach everyone.
- Five corners add the state beside the exchange; clearance puts it in the middle.
- A group lives in several models at once: design one framework for all.
How We Help
Route map
Every entity and country placed in its model, with the provider and data each needs.
Implementation
SAP DRC configured for each route: sending, receiving and statuses in one cockpit.
Run
Directory entries, providers and legal change kept current.
Where Do Your Entities Sit?
Bring your list of companies and the countries they invoice in to our free 60-minute diagnostic: you leave with a route map of corners, providers and dates.
Sources consulted 13 October 2026: OpenPeppol and national Peppol authorities; Digital Agency (Japan); IRAS and Avalara on GST InvoiceNow (Singapore); European Commission on ViDA; 30 Advisory country briefings (Belgium, France, Germany, Italy, Poland, Spain, UAE and Japan) and the sources cited in them. Examples are illustrative; the group in section 07 is fictitious.
Prepared by 30 Advisory. Educational document; not tax, legal or accounting advice. Country positions are simplified and change frequently. Confirm the treatment of any real case with a qualified adviser. 30 Advisory accepts no liability for decisions taken on the basis of this document.