GST and InvoiceNow readiness guide

1. Create a client-owned registration-history register

Assign a client register owner, a GST adviser, an Oakland delivery lead and a compliance reviewer before entering data. Use controlled tabs for legal entities and branches, registration history, filing periods, source documents, adviser decisions and evidence owners. Every row carries a stable entity ID, status, source location, reviewer and revalidation date; no access secret belongs in the register.

• Field group: Legal identity; Minimum entries: Legal and trading names, UEN, incorporation date and constitution; Owner: Client entity owner
• Field group: GST history; Minimum entries: Voluntary-application dates, compulsory-registration history, GST groups, deregistration and re-registration; Owner: GST owner and adviser
• Field group: Filing history; Minimum entries: Filing frequency, special periods, approved extensions and historical rates or codes; Owner: Return owner
• Field group: Evidence; Minimum entries: IRAS notices, branch relationships, source location, reviewer and revalidation date; Owner: Named evidence custodian

Synthetic acceptance example: Entity A has a voluntary registration interval, a later compulsory interval and a branch whose staff use a different trading name. The register owner must produce both registration notices, the branch relationship and a filing-period calendar. A completed Odoo company record alone is not accepted as registration proof.

Reviewed 6 November 2026 — research review, not legal signoff. Revalidation owner: Compliance reviewer (CR) with the country owner and named client advisers; unresolved human Singapore regulatory review by a qualified Singapore regulatory reviewer remains mandatory before release.

2. Build the transaction register from source documents

Select real but redacted invoices, credit notes, supplier bills and receipts, then create synthetic training copies. Record the actual place-of-supply and time-of-supply analysis before configuring a tax code. The IRAS current-rate source supports 9% only for applicable standard-rated supplies.

Use the GST overview and General Guide, 17th edition dated 30 January 2026 to distinguish standard-rated, qualifying zero-rated, exempt and out-of-scope treatment. Zero-rated exports or international services require their qualifying evidence; exempt supplies are not renamed zero-rated for convenience.

• Evidence group: Document; Minimum entries: Entity, branch, document ID, type, supply description and source attachment; Acceptance owner: AP/AR owner
• Evidence group: Supply analysis; Minimum entries: Invoice and supply dates, destination evidence, place and time of supply; Acceptance owner: GST adviser
• Evidence group: Tax result; Minimum entries: Category, tax code, GST amount, return period and reporting box; Acceptance owner: GST reviewer
• Evidence group: Decision; Minimum entries: Adviser rationale, evidence owner, review date and open question; Acceptance owner: Client decision owner

Synthetic acceptance uses a local consulting invoice, an exported-goods invoice with destination evidence, a financial-service sample reviewed for exemption and a shareholder transaction assessed as out-of-scope. The adviser records the reasoning for each, and the GST reviewer accepts document, journal and report results together.

3. Record Box 13, imported services and reverse-charge logic

Under the General Guide, out-of-scope transactions are entered in Box 13 only when they form part of revenue; otherwise they are omitted. Conditional Box 13 treatment must cite the transaction's revenue analysis. It must not be merged with zero-rated or exempt sales, and no default tax code may put every out-of-scope row in that box.

The IRAS local-business digital-economy guidance covers imported services since 2020 and low-value goods since 2023. Reverse charge is relevant only where the applicable input-tax restrictions and eligibility conditions apply, not to every overseas purchase.

• Review field: Out-of-scope rationale and revenue condition; Why it is required: Supports inclusion in or omission from Box 13; Owner: GST adviser
• Review field: Imported-service or low-value-goods facts; Why it is required: Establishes the relevant digital-economy analysis; Owner: AP owner and adviser
• Review field: Input-tax restriction and eligibility; Why it is required: Determines whether reverse charge is relevant; Owner: GST adviser
• Review field: Permit, financial or DPT review; Why it is required: Supports InvoiceNow exclusion analysis where applicable; Owner: GST reviewer

Synthetic acceptance requires one eligible imported-service case and one overseas purchase that fails the relevant condition, each with the adviser's reasoning and resulting entry rather than an automatic rule.

4. Establish the exact trigger with the phase table

The requirement takes effect in phases. Do not treat it as a single current mandate for every GST-registered business.

• Published trigger and scope: Active from 1 November 2025: companies applying for voluntary GST registration on or after that date and within six months of incorporation.; Evidence to retain: Application date, incorporation date and IRAS registration evidence
• Published trigger and scope: Active from 1 April 2026: businesses applying for voluntary GST registration on or after that date, regardless of incorporation date or constitution.; Evidence to retain: Application date, constitution and IRAS registration evidence
• Published trigger and scope: From 1 April 2028: all new compulsory GST registrants and existing businesses with annual supplies up to S$200,000.; Evidence to retain: New-compulsory status or existing-business Box 4 schedule
• Published trigger and scope: From 1 April 2029: existing businesses with annual supplies up to S$1 million.; Evidence to retain: Box 4 schedule and entity-specific IRAS notification or calculator result
• Published trigger and scope: From 1 April 2030: existing businesses with annual supplies up to S$4 million.; Evidence to retain: Box 4 schedule and entity-specific IRAS notification or calculator result
• Published trigger and scope: From 1 April 2031: existing businesses with annual supplies of more than S$4 million.; Evidence to retain: Box 4 schedule and entity-specific IRAS notification or calculator result

For existing businesses, annual supplies means the Box 4 total of standard-rated, zero-rated and exempt supplies across all prescribed accounting periods ending in calendar year 2025. Record each period and entity-specific IRAS notification and calculator evidence; do not infer a phase from revenue alone.

Use the IRAS requirement page, FAQ amended 26 October 2026 and IMDA factsheet dated 27 February 2026. The phase register stores application and registration dates, incorporation and constitution facts, each prescribed accounting period, Box 4 source workpapers, notification ID, calculator output, reviewer and open question.

Synthetic acceptance assesses a newly incorporated voluntary applicant against its application evidence and an existing business against the prescribed-period supply schedule. The unresolved human Singapore regulatory reviewer confirms the final phase interpretation before release.

5. Prove the exact solution, activation and provider scope

Covered businesses need an InvoiceNow-Ready Solution with the GST submission feature activated. A Peppol ID, network membership or access-point identifier alone is insufficient. Record provider legal name, exact product and version, hosting arrangement, solution owner, access-point provider, endpoint identifiers, feature setting, activation evidence, test environment, production owner, support route and credential custodian without storing secrets.

Review the SFFS framework, the SFFS Odoo page and the InvoiceNow-Ready Solution Provider list updated 12 October 2026. Capture the exact listing row, product name, expressly named API scope, retrieval date and limitations.

The SFFS Odoo page developed by Port Cities Singapore Pte. Ltd. lists InvoiceNow-Ready only; it is not evidence for core Odoo, Odoo S.A., Oakland or F5/F7/F8. Other SFFS and InvoiceNow-Ready Solution Provider (IRSP) rows verify only the expressly named provider products and APIs, not endorsement, security or statutory compliance.

• Acceptance layer: Product identity; Minimum evidence: Provider, product, version and exact listing row; Owner: Client solution owner
• Acceptance layer: Activation; Minimum evidence: GST submission feature enabled in the intended environment; Owner: Provider and client administrator
• Acceptance layer: Connectivity; Minimum evidence: Access-point identifiers, test transmission and support route; Owner: Provider connectivity owner
• Acceptance layer: Governance; Minimum evidence: Credential custodian, custom connector boundary and revalidation date; Owner: Client system owner

A screenshot of a Peppol ID is not acceptance evidence. Require a provider-led activation test with a covered synthetic invoice, visible transmission status and a named client owner.

6. Separate Odoo 19 PINT-SG file support from transport and filing

The Odoo 19 localization catalogue, Singapore page and l10n_sg manifest identify the core product baseline. Review the Boxes 1–21 report data and tax templates against the approved entity and transaction map. Chart, UEN, permit, GST and report data require fine-tuning and do not prove direct F5, F7 or F8 filing.

The l10n_sg_ubl_pint manifest, generation and import implementation and partner fields support PINT-SG data work. PINT-SG XML generation or import is not transport, provider connectivity or an IRAS connector.

Singapore is absent from the reviewed lists of countries eligible for Odoo-operated Peppol registration in Odoo 19 and Odoo 20. This is not a statement that Singapore businesses cannot use Peppol; the separate provider and access-point path must be proven.

In the Odoo electronic-invoicing workflow, Done means delivery to the contact's access point. It does not mean buyer acceptance, IRAS approval or GST submission. Acceptance separates XML schema and field tests, provider transport, solution GST submission, acknowledgement retrieval and accountant return review into distinct signed rows.

7. Map included invoice data and both non-Peppol paths

InvoiceNow scope covers standard-rated supplies and purchases, zero-rated supplies and purchases, and exempt supplies only; there is no general exempt-purchase category. A mixed invoice retains line-level categories rather than one header category imposed across all lines.

The exclusion review covers reverse-charge transactions, import permits and specified financial and digital-payment-token cases in current IRAS material. Distinguish businesses excluded because of their particular registration basis from ordinarily registered businesses that merely have reverse-charge transactions.

• Data path: Network sales and purchases; Required source and extraction evidence: Original document, line categories, identifiers and accounting link; Submission and acceptance evidence: Submission ID, acknowledgement and GST reviewer
• Data path: Sales invoices issued outside the Peppol network; Required source and extraction evidence: Original invoice, solution extraction method, extraction owner and field-confidence review; Submission and acceptance evidence: Duplicate check, accounting link, submission and acknowledgement
• Data path: Purchase invoices recorded in the solution; Required source and extraction evidence: Original supplier invoice, recording owner, field-confidence review and supplier identity; Submission and acceptance evidence: Duplicate check, accounting link, submission and acknowledgement
• Data path: Paper or PDF handoff; Required source and extraction evidence: Preserve the original and create a reviewed solution entry; Submission and acceptance evidence: Access Points do not convert paper or PDF documents into Peppol invoices; the solution and user own extraction and review

For both non-Peppol paths, preserve originals, extraction owner, field-confidence review, duplicate controls, accounting link, submission and acknowledgement. A supplier's transmission to its customer does not remove the buyer's own required purchase-data and input-tax evidence responsibilities.

Synthetic acceptance uses a standard-rated sale, a qualifying zero-rated line, an exempt supply line, an excluded permit-related sample, an off-network sales invoice and a recorded supplier bill. The GST reviewer signs category and exclusion decisions; the provider signs extraction and transmission behaviour; accounting signs resulting entries and source links.

8. Control aggregation, filing timing and the five-year archive

Where current IRAS rules allow aggregation, create separate rules for POS sales, simplified invoices and petty-cash purchases, including staff claims and corporate-card purchases where applicable. Preserve transaction-level evidence behind every aggregate.

• Control: Aggregation; Minimum entries: Rule version, outlet or cost owner, business date, source count, included and excluded IDs; Owner: Outlet or AP owner
• Control: Tax totals; Minimum entries: Standard-rated, zero-rated and exempt supply totals and exclusions; Owner: GST reviewer
• Control: Filing timing; Minimum entries: Actual filing date, return due date, selected earlier date and submission timestamp; Owner: Return owner
• Control: Archive; Minimum entries: Source documents, aggregate payload, acknowledgement history and retrieval test; Owner: Evidence custodian

Send the invoice data by whichever comes first: the date the relevant GST return is actually filed or that return’s filing due date. Record both candidate dates, the selected control date, solution submission timestamp, delay reason and exception owner.

The IRAS due-date source says returns and payment are usually due one month after the accounting period, while special periods and approved extensions remain separate. GST-return filing and payment continue.

IRAS recordkeeping guidance generally requires records for at least five years. Name the archive location, source documents, payload versions, acknowledgement history, return workpapers, retention owner, access review and retrieval test. Acceptance requires retrieving one complete synthetic transaction pack without provider assistance.

9. Reconcile acknowledgement, correction and exception evidence

An acknowledgement confirms receipt. It is not buyer acceptance, confirmation of tax treatment, a GST return or payment. It also does not establish IRAS clearance or bank reconciliation.

• Evidence field: Solution batch and document IDs; Purpose: Connects source, aggregate and accounting records; Owner: Solution operator
• Evidence field: Submission and acknowledgement timestamps; Purpose: Supports timing and exception review; Owner: GST reviewer
• Evidence field: Source hash and correction version; Purpose: Prevents unreviewed overwriting; Owner: Data owner
• Evidence field: Retry and latest acknowledgement; Purpose: Shows the complete correction history; Owner: Provider and GST reviewer

Build a synthetic rejection and correction exercise: introduce a controlled invalid field in a test environment, record the provider error, assign the data owner, correct the source, resubmit without duplicating accounting documents and match the new acknowledgement to the latest version. Preserve both attempts and their statuses.

Reconcile source invoices, accounting entries, solution submission list, acknowledgement list and GST-return workpapers. Investigate missing acknowledgements, duplicate references, changed categories and late corrections. The provider accepts connectivity and status behaviour; the GST reviewer accepts data scope and corrections; the return owner separately signs filing evidence.

10. Issue a stop/go pack with named unresolved owners

The final register groups blockers by registration history, supply treatment, phase, annual-supply evidence, provider product, feature activation, connectivity, invoice scope, exclusions, aggregation, acknowledgement, filing and archive. Each row states the question, missing evidence, client owner, adviser, provider or Oakland owner, due decision and release effect.

Run the prototype with redacted source documents and synthetic training cases, then retain mappings, XML or payload samples, provider results, acknowledgements, correction logs, return workpapers and archive retrieval evidence. Provider, access-point and session-company examples are educational only, never Oakland references, recommendations, Singapore delivery evidence or proof of statutory capability.

The September 2026 Odoo 20 release notes describe Odoo 20 additions for Singapore tax invoices, credit notes, customer-accounting PDFs and Singapore Financial Reporting Standards (SFRS). Do not infer them into Odoo 19 or claim categorically whether they were backported: compare the actual Odoo 19 and Odoo 20 manifests and views and test the deployed build.

Use the release notes, Odoo 19 l10n_sg views and Odoo 20 l10n_sg views for that comparison. Directory presence alone is not a feature claim; the deployed build needs its own acceptance evidence.

Continue with the SGD migration and reconciliation guide, POS go-live and recovery checklist and payroll boundaries and role-training guide. The unresolved qualified Singapore regulatory review remains a release gate, not a footnote replaced by this research review.