Peppol 5-corner model and IRAS tax reporting
How InvoiceNow extends the standard 4-corner Peppol model to a 5-corner model with IRAS as the fifth participant — what gets reported, when and how it lines up with the F5 return.
The classical Peppol model has four corners: the seller's billing system (C1), the seller's Access Point (C2), the buyer's Access Point (C3) and the buyer's accounting system (C4). For Singapore, IRAS extends this with a fifth corner — itself — receiving an InvoiceNow Tax Report (ITR) from the seller's Access Point in near real time. This 5-corner architecture is what turns InvoiceNow from a pure B2B network into a continuous transaction control (CTC) regime similar in spirit to (but lighter than) Italy's SDI, Hungary's NAV online szamla or Vietnam's GDT. It preserves the speed and interoperability of Peppol while giving IRAS a structured data feed for GST compliance.
- Corner 5: IRAS receives an InvoiceNow Tax Report from C2.
- Latency: near real time, typically within minutes of transmission.
- Scope: in-scope GST-registered businesses under the IRAS mandate.
- Reconciliation: F5 boxes pre-populated from the 5-corner feed.
How it works
The seller's billing system generates a Peppol UBL XML invoice with SG PINT extensions and hands it to its Access Point (C2). This is the standard Peppol C1→C2 step — no special configuration is needed beyond using an IMDA-approved AP and the correct SG PINT customisations for GST treatment codes and the supplier's UEN/GST registration number.
The Access Point routes the invoice to the buyer's Access Point (C3) via the AS4 protocol over the Peppol network. IMDA's Service Metadata Publisher (SMP) and Service Metadata Locator (SML) resolve the buyer's UEN under the 0195:SGUENT scheme to the right C3 endpoint. The buyer's accounting system (C4) receives the UBL XML, validates against the SG PINT schematron and books the invoice — this is the unchanged C2→C3→C4 chain.
In parallel, the seller's Access Point forwards an InvoiceNow Tax Report to IRAS as the fifth corner. The ITR is a constrained subset of the original invoice — GST registration number, GST treatment per line, totals, customer UEN, invoice number, date — designed to give IRAS what it needs for compliance without exposing every commercial detail. The transmission is again over AS4 with the AP's Peppol certificate authenticating the sender.
IRAS ingests the ITR into its tax data pipeline and matches it against the seller's GST registration record. For mandated participants, this data progressively replaces manual F5 input — over time, the GST return becomes a reconciliation against the ITR feed rather than a fresh declaration. Discrepancies (e.g. an invoice transmitted on InvoiceNow but not declared on F5, or vice versa) trigger automated nudges and, eventually, audit triggers.
Credit notes and amendments flow through the same 5-corner pipeline. A credit note follows the original invoice on Peppol (C1→C2→C3→C4) and the matching ITR adjustment goes to IRAS (C2→C5). This keeps the IRAS view continuously aligned with the commercial truth between buyer and seller — no batch reconciliation, no quarterly catch-up. From a buyer's perspective, the only visible change vs. classical Peppol is that the seller is now known to be reporting to IRAS, increasing the reliability of input GST claims.
Legal framework
- Goods and Services Tax Act 1993 (Cap. 117A) — invoicing and records.
- IRAS e-Tax Guide: Adoption of InvoiceNow Requirement for GST-Registered Businesses.
- IMDA appointment as Peppol Authority for Singapore (May 2018).
- OpenPeppol PINT specification and SG PINT customisation guide.
Frequently asked questions
Why does Singapore use a 5-corner model instead of a clearance model like Italy?
Italy's SDI is a pre-clearance model: every invoice must be approved by the tax authority before it reaches the buyer. That works but adds latency, single-point-of-failure risk and a hard dependency on government uptime. Singapore chose a post-transmission reporting model: the invoice flows on Peppol independently of IRAS, and IRAS receives a parallel data feed. The buyer's input GST is not gated on IRAS availability — the network remains operational even during IRAS maintenance windows. It is a CTC regime, but a lighter one.
What exactly does IRAS see on each invoice?
The InvoiceNow Tax Report contains: seller's GST registration number and UEN, buyer's UEN (or country code if foreign), invoice number, invoice date, totals (taxable amount, GST amount, total payable), per-line GST treatment codes (standard 9%, zero-rated, exempt, out-of-scope), and exemption reason codes for zero-rated/exempt lines. IRAS does NOT see free-text descriptions of goods/services in the ITR — those stay between buyer and seller in the full UBL XML. This balances tax oversight with commercial confidentiality.
Will the F5 return disappear once InvoiceNow is mandatory?
Not in the short term. The F5 remains the legal GST return, but IRAS has stated that progressive pre-population of F5 boxes from InvoiceNow data is part of the medium-term roadmap. In the first phase (from 1 May 2025), in-scope businesses still file the F5 manually as before — InvoiceNow runs alongside. Over subsequent years, the F5 is expected to evolve into a confirmation/reconciliation form rather than a data-entry form, similar to the trajectory seen in Italy with the pre-compiled VAT return.
What about B2C transactions — are those also in the 5-corner flow?
Not directly. The Peppol network is designed for B2B (and B2G) where both parties have an addressable endpoint. B2C transactions to consumers do not go through Peppol because consumers do not have UENs. For B2C, GST-registered businesses continue to issue receipts/simplified tax invoices and aggregate B2C sales in the F5 return manually. IRAS may extend reporting to B2C in future via POS integration, but that is not part of the current 5-corner InvoiceNow scope.
How does the 5-corner model affect non-Singapore counterparties?
Cross-border invoices on Peppol — for example a Singapore seller to a German buyer — still flow through the standard 4-corner model (Peppol is international by design). The fifth corner (IRAS reporting) applies only on the seller side and only if the seller is a GST-registered Singapore business in the scope of the mandate. The German buyer sees nothing different from a classical Peppol BIS invoice. Similarly, a German seller invoicing a Singapore buyer does not need to report to IRAS — only Singapore-resident sellers do.