A tax invoice is not a design decision. Rule 46 of the CGST Rules sets out what has to be on it, and the reason to care is not the penalty — it is that your customer cannot claim input tax credit against an invoice that is missing a required field. That turns a formatting slip into a commercial problem, and you usually hear about it from the customer's accountant rather than from your own.
The required set is short enough to memorise: your name, address and GSTIN; a consecutive invoice number unique within the financial year; the date; the recipient's name, address and GSTIN where registered; HSN or SAC codes; a description, quantity and unit; taxable value after discount; the rate and amount of tax under each head; the place of supply where the supply is inter-state; and a signature or digital signature.
Two rules cause most of the trouble in practice. The invoice number must be consecutive and unique within the financial year — which quietly rules out restarting your numbering mid-year, or running one shared series across branches without a distinguishing prefix. And the tax must be broken out by head and by rate, not presented as a single blended figure.
Key takeaways
- A missing mandatory field can cost your customer their input tax credit, not just you a penalty.
- Invoice numbers must be consecutive and unique within the financial year.
- Tax has to be shown per head and per rate, never as one blended line.
- Place of supply is a required field on inter-state invoices — state it explicitly.
- HSN or SAC codes are required; the digit depth expected varies with turnover.
Practical checklist
- Audit one invoice against every field in Rule 46, line by line.
- Confirm your numbering series cannot repeat or skip across branches.
- Check that multi-rate invoices break tax out per rate, not per invoice.
- Ask your largest customer's accounts team whether anything has ever been queried.
What to do next week
Most of this is the kind of correctness a template should guarantee rather than something you re-check by hand each month. Envocify generates invoices with the mandatory fields built into the document — numbering series per branch, tax broken out by head and rate, HSN and SAC on the line. If you would rather look at the output than take our word for it, the product page shows a worked example.
How we work with clients at TechTrio
Every engagement at TechTrio Automation starts with a short discovery phase: we map your current stack, traffic, conversion paths, and operational bottlenecks. From there we propose a phased roadmap — quick wins first (tracking, analytics hygiene, performance, or a focused automation), then deeper builds (product modules, integrations, or marketing systems). Our teams in Ahmedabad and Mehsana collaborate closely with stakeholders in India, the UK, USA, Canada, and the UAE, so documentation, handoffs, and support hours stay practical.
We bias toward maintainable defaults: typed frontends where it pays off, predictable hosting on Vercel or similar for marketing sites, Firebase or Postgres depending on data and compliance needs, and observability so you are never guessing whether a workflow ran. Security is not an afterthought — least-privilege access, secrets outside the repo, and reviews for anything that touches payments or personal data.
If you are evaluating an agency or studio partner, ask for references in your industry, a clear definition of done, and a plan for what happens after launch. We publish these articles because we want founders and operators to make better decisions — whether or not you ever hire us. When you are ready for a deeper conversation, book a short session from our site and we will help you prioritise what to build, automate, or measure next.
Published by TechTrio Automation — web, mobile, SaaS, and AI automation from Gujarat, serving teams worldwide.
Related reading
- Getting the CGST, SGST and IGST split right
- IRN and e-way bills, explained without the jargon
- How to choose GST invoicing software
Frequently asked questions
Can I restart my GST invoice numbering during the year?
No. The series must be consecutive and unique within a financial year. You can start a fresh series at the beginning of a new financial year, and you can run distinct series per branch provided each is uniquely identifiable.
What happens if a mandatory field is missing?
The most immediate consequence is commercial rather than punitive: your customer may be unable to claim input tax credit against a defective invoice, which usually means they ask you to reissue it.
Do I need HSN codes on every invoice?
HSN for goods and SAC for services are required, and the number of digits expected depends on turnover. Check the current requirement for your slab on the GST portal, since it has been revised.
