Technical Requirements and Mandatory Data

🎯 Purpose

This document outlines the mandatory data, technical requirements, and integration expectations for organisations connecting to Link4 to send and receive electronic invoices and related documents.

This guide explains the mandatory technical and data requirements for organizations integrating with Link4 to send and receive electronic invoices.

Before integration, ensure your ERP, Accounting System, or Middleware can supply all required data.

1. invoice rejection
   
2. validation errors
   
3. delivery failures with authorities such as Peppol Singapore (IMDA) or Peppol networks

1️⃣ Supported Integration Method

API Integration

Your system connects to Link4 via a secure API.

Requirements

• API endpoints provided by Link4

• OAuth or API key Authentication

• Valid JSON Payload structure 
  

• Data validation compliance

2️⃣ Supported Transaction Types

01. Invoices

• Peppol Sales Invoice (PINT)

• Peppol Sales Invoice (PINT) in Foreign Currency

• Peppol Sales Invoice (BIS)

• Non-Peppol Sales Invoice

• Aggregated B2C sales Invoice

02. Credit Notes

• Peppol Sales Credit Note (PINT)

• Peppol Sales Credit Note (BIS)

• Non-Peppol Sales Credit Note in Foreign Currency

• Non-Peppol Purchase Credit Note

• Peppol purchase Credit Note

03. Purchase

• Non-Peppol Purchase Invoices

• Aggregated PCP purchase Invoice
  

For all document types, the following data must be complete

• Document header data

• Supplier and buyer details

• Line items

• Tax information
  

3️⃣ Contact Data Requirements (Buyers & Suppliers)

Accurate contact data is mandatory.

This data is used for:

• Addressing and routing (Peppol)

• Tax authority validation (e.g. IMDA)

• Delivery and notifications

3.1 Mandatory Fields (Per Contact)

Applies to BOTH buyers and suppliers.

3.2 Optional but Recommended

• Trading name

• Email address

• Phone number

• Contact person name

• Department name

• GST registration number (if different from UEN)

• Website

• Internal reference code

3.3 How to Provide Contact Data

Option A – API

• Each contact must be retrievable using a unique identifier

• All mandatory fields must be returned

• Used to avoid duplicates and ensure correct matching

Option B – CSV Upload

• CSV must include all mandatory fields

• A unique reference column may be required for create/update logic

• Column order and format will be confirmed by Link4

4️⃣ Tax Information

Tax data must comply with the target jurisdiction (e.g. IMDA, Peppol VAT rules).

4.1 Document (Header) Level – Mandatory

• Supplier UEN

• Buyer UEN

• Currency = SGD

• GST 9%

5️⃣Line Item Requirements

Each invoice, credit note, debit note, or self-billed document must include at least one valid line item.

Required

• Description

• Quantity

• Unit

• Unit price

• Line amount

• GST rate

• GST amount

Optional

• Product ID

• Discount

• Order line reference

• Contract reference

6️⃣  Document Header Requirements

Mandatory

• Unique document number

• Issue date (YYYY-MM-DD)

• Document type (Invoice / Credit Note / Debit Note)

• Supplier details (UEN, legal name, full address)

• Buyer details (UEN or Peppol ID, legal name, full address)

• Currency (SGD unless otherwise agreed)

• Tax-exclusive amount

• Total GST amount

• Tax-inclusive amount

Optional

• Due date

• Order reference (PO number)

• Buyer reference

• Contract or project reference

• Payment terms

• Bank / payment details

• Delivery date

• Internal notes (must comply with Peppol format rules)

7️⃣ API Integration Requirements

Authentication

• Secure credentials (OAuth or API keys)

• Required permissions for read and write operations

Data Coverage

• Header data

• Line items

• Tax information

• Contact data resolvable via unique IDs

Behaviour

• Duplicate documents must be avoided

• Clear error responses (HTTP status + message)

• Stable document identifiers for retries and reprocessing

8️⃣ Validation & Submission

All documents are validated against:

• Peppol BIS 3.0

• IMDA routing via UEN

Missing or invalid data may result in:

• Document rejection

• Validation errors

• Delivery failure (e.g. buyer not on network)