The Peppol 5-Corner Model: How IRAS Becomes the Fifth Corner

To understand the GST InvoiceNow Requirement, it helps to understand the network model behind it. InvoiceNow runs on Peppol's four-corner model; the GST requirement adds a fifth corner - IRAS.

The four-corner model

Peppol's classic model connects four parties:

• •Corner 1 - the supplier, who creates a structured invoice in their accounting or ERP system
• •Corner 2 - the supplier's Access Point, which transmits the invoice over the Peppol network
• •Corner 3 - the buyer's Access Point, which receives and delivers the invoice
• •Corner 4 - the buyer's system, which processes the invoice automatically

Adding the fifth corner

The GST InvoiceNow Requirement introduces Corner 5: a copy of the structured invoice data is transmitted to IRAS for GST reporting. When you send an invoice through an InvoiceNow-Ready solution, the relevant data flows to IRAS by the filing date of the related GST return - without a separate manual submission.

From periodic returns to continuous controls

This is a structural shift. Traditional GST reporting is periodic - you file a return each accounting period. The five-corner model moves Singapore towards continuous transaction controls (CTC), where the tax authority receives transaction data close to when it happens. It is the clearest sign yet of where Singapore's tax administration is heading.

What changes for you

Practically, the fifth corner is handled by your accredited solution - you do not build a separate IRAS connection. But it does mean your invoice data must be complete and correct at the point of transmission, because it now serves both your trading partner and your GST reporting.

Why this design is good for business

Because IRAS receives structured data directly, returns can be cross-checked automatically against transactions. Over time this can mean fewer manual audits and faster verification for refund claims - particularly for zero-rated exporters whose claims are supported by data already on record.