Integrated Business Solutions (Multidisciplinary Case Study with Strategic Management) · Indirect Tax Laws

GST Registration, Invoicing, Returns and Payment for CA Final

Updated 5 October 2026

This topic covers the GST procedures: who must register, how to issue tax invoices, credit and debit notes, when e-invoice and e-way bill apply, which returns to file, how to pay tax and how to claim refunds. Solve questions by identifying the rule, applying the case facts, checking time limits, and stating a clear conclusion.

Understand GST Registration, Invoicing, Returns and Payment

GST law has two halves. One half decides what is taxable. The other half is procedure: how a person enters the system, documents supplies, reports them, pays tax and gets money back. This topic is the procedure half. Exam cases test whether you can spot which procedural rule is triggered by the facts.

Registration. A person making taxable supplies must register once aggregate turnover crosses the threshold in the law. Some persons must register whatever their turnover, such as persons making inter-State taxable supplies of goods (with limited exceptions), casual taxable persons, non-resident taxable persons, e-commerce operators and persons liable to pay tax under reverse charge. Check the exact threshold and the exceptions for special category States and for services in the official text supplied to you. Registration is State-wise and PAN-based, so a business with places in several States needs a registration in each State.

Documents. A registered supplier issues a tax invoice for taxable supplies. A registered person who receives goods or services from an unregistered supplier may have to raise a self-invoice if tax is payable under reverse charge. A credit note is issued when the taxable value or tax in an invoice is more than what is correct, or for returns or deficiency. A debit note is issued when it is less. E-invoicing means the invoice details are uploaded to the Invoice Registration Portal, which returns an IRN and a QR code. It applies to notified registered persons above the notified turnover limit, so always check the current limit and the exempted classes. An e-way bill is needed for movement of goods of a consignment value above the prescribed limit, subject to exemptions.

Returns and payment. GSTR-1 reports outward supplies. GSTR-3B is the summary return in which you report liability, claim ITC and pay tax. Tax is paid through the electronic cash ledger, and ITC sits in the electronic credit ledger. The order in which ITC is used against IGST, CGST and SGST is fixed by law, and the cash ledger covers what ITC cannot. Interest is payable on late payment.

Refunds. Refund claims arise from zero-rated supplies, inverted duty structure, excess cash balance, and tax paid by mistake, among others. Refund is claimed within the time limit in the law, normally two years from the relevant date. Refund of unutilised ITC on zero-rated supplies made without payment of tax is allowed under section 54(3)(i). Zero-rated supply is covered by section 16 of the IGST Act, which allows export with or without payment of IGST. Refund of IGST paid on exports is claimed under section 16(3)(b) of the IGST Act read with section 54 of the CGST Act. In an inverted duty structure, the tax rate on inputs is higher than the rate on output supplies (other than nil-rated or fully exempt supplies). Refund of unutilised ITC in that case is allowed under section 54(3)(ii), subject to conditions and to exclusions notified by the Government, which you must check in the official text. The formula in the Rules limits the amount. In that formula, Net ITC means ITC availed on inputs and input services. ITC on capital goods is not part of it.

Key rules to remember

Aggregate turnover: Aggregate turnover = taxable supplies + exempt supplies + exports of goods/services (inter-State supplies are already included within these), computed on all-India basis for persons with the same PAN, excluding inward supplies on reverse charge, excluding the value of outward supplies on which tax is payable by the recipient under reverse charge, and excluding CGST, SGST, UTGST, IGST and cess; Used for registration threshold, e-invoicing limit and composition checks. Inter-State supplies are not a separate add-on. Both inward supplies on reverse charge and outward supplies on which the recipient pays tax under reverse charge are left out. Check inclusions and exclusions in the official text.
Credit note versus debit note: Invoice value or tax too high or goods returned → credit note; invoice value or tax too low → debit note; Both adjust the original invoice and are reported in the return.
Refund for inverted duty structure: Maximum refund = [Turnover of inverted rated supply of goods and services × Net ITC ÷ Adjusted total turnover] − tax payable on such inverted rated supply of goods and services, as per Rule 89(5); Learn the structure and use the values given in the question. Net ITC means ITC availed on inputs and input services, not capital goods. There is no second factor on the tax payable: you deduct the tax payable on the inverted rated supply in full.
Time limit for refund: Application within 2 years from the relevant date; The relevant date differs by type of refund, so identify the type first.
Return mapping: GSTR-1 = details of outward supplies; GSTR-3B = summary return with payment of tax; GSTR-1 gives the recipient's ITC data. GSTR-3B is where tax is paid.

How to solve GST Registration, Invoicing, Returns and Payment questions

Use this approach for any case on registration, documents, returns, payment or refund.

1Read the question and mark the issue type: registration, invoice, e-invoice, e-way bill, return, payment or refund.
2Pick out the facts that trigger a rule: turnover, type of supply, place of business, goods value, dates, status of recipient.
3State the rule in one or two sentences, with exact thresholds or time limits from the official text.
4Check exceptions and special cases, such as special category States, notified persons or exempt goods.
5Apply the rule to the numbers: compute aggregate turnover, count days, or check order of ITC use.
6Write the conclusion in one clear line, for example 'registration is compulsory from the date he becomes liable'.
7For written answers, use the form provision, facts, conclusion. For MCQs, eliminate options that mix the wrong threshold or document.

Quickest way: Trigger-and-Limit check

When to use it: Use for MCQs and short case parts where you have only a few minutes.

Underline the trigger word: inter-State, reverse charge, casual, e-commerce, export, return, inverted.
Recall the one limit or rule attached to that trigger.
Compare it with the figure in the case.
Check one exception.
Choose the option or write the one-line conclusion.

Common mistakes in GST Registration, Invoicing, Returns and Payment

Applying the registration threshold to a person who must register compulsorily.
Students remember the turnover limit and treat it as universal.
Fix: First test the compulsory categories such as casual, non-resident, e-commerce operator and reverse charge. Use the threshold only after that.
Counting reverse charge inward supplies or taxes in aggregate turnover.
Students add all values in the books without applying the definition.
Fix: Take values as per the definition and exclude taxes and inward supplies on reverse charge.
Treating GSTR-1 as the return that pays tax.
Both returns are filed monthly and have similar names.
Fix: Remember: GSTR-1 reports sales, GSTR-3B pays tax and claims ITC.
Issuing a credit note when value goes up, or a debit note when value goes down.
Students think from their own books instead of from the invoice.
Fix: Ask whether the original invoice must go down or up. Down means credit note, up means debit note.
Claiming refund of ITC for exempt or nil-rated output under inverted duty.
Students see unutilised ITC and assume refund.
Fix: Check that the input tax rate is higher than the output rate, that the output is not nil-rated or fully exempt, and that no notified exclusion applies.
Ignoring the time limit for refund or the relevant date.
Students focus on the amount, not the date.
Fix: Identify the type of refund, find its relevant date, then count the two-year period.

Worked examples

Example 1

Ravi Traders, based in one State, supplies only taxable goods within that State. His turnover in the year is below the threshold applicable to his State. He also begins to supply goods inter-State to a customer. Must he register?

Show the solution

Issue: whether registration is compulsory when turnover is below threshold.
Rule: a person making inter-State taxable supplies of goods must register irrespective of turnover, subject to exceptions notified for certain suppliers.
Facts: Ravi makes inter-State taxable supplies of goods and no exception is mentioned.
Application: the threshold test is not relevant for him once he makes such supplies.
Conclusion: he must register as soon as he makes the inter-State supply.

Answer: Yes. Inter-State taxable supply of goods makes registration compulsory despite low turnover, unless a notified exception applies.

Example 2

A manufacturer makes only one kind of taxable goods, supplied at 5% GST, with a turnover of ₹30,00,000 in the relevant period. Inputs are taxed at 18%. The ITC availed on inputs is ₹3,00,000 and the ITC availed on input services is ₹1,00,000, so Net ITC is ₹4,00,000. The tax payable on the output supply is ₹1,50,000 (5% of ₹30,00,000). There is no other turnover. Find the maximum refund under the inverted duty structure formula.

Show the solution

Issue: refund of unutilised ITC under the inverted duty structure.
Rule: maximum refund = [Turnover of inverted rated supply × Net ITC ÷ Adjusted total turnover] − tax payable on such inverted rated supply. Net ITC means ITC availed on inputs and input services.
Facts: turnover of inverted rated supply = ₹30,00,000; adjusted total turnover = ₹30,00,000; Net ITC = ₹3,00,000 + ₹1,00,000 = ₹4,00,000; tax payable on the inverted rated supply = ₹1,50,000.
Step 1: (₹30,00,000 × ₹4,00,000) ÷ ₹30,00,000 = ₹4,00,000.
Step 2: deduct the tax payable on the inverted rated supply: ₹4,00,000 − ₹1,50,000 = ₹2,50,000.
Interpretation: the whole supply is inverted rated, so the full Net ITC is the starting figure. The refund is the part of that ITC that the tax payable on the output cannot absorb.

Answer: Maximum refund is ₹2,50,000, subject to the claim being made within two years from the relevant date and no exclusion applying.

Exam tips

In case MCQs, read the last line first so you know whether the question asks about registration, document or refund.
Always quote the threshold or limit from the official text given to you, and never rely on old figures.
Write a short table-free calculation for aggregate turnover and refund formula questions so you earn step marks.
For return questions, name the return and what it does in one sentence.
In Paper 6, link the procedure to the business: for example, how e-invoicing or refund delays affect working capital.

Practice questions from Indirect Tax Laws

GST Registration, Invoicing, Returns and Payment: frequently asked questions

What is the difference between GSTR-1 and GSTR-3B?

GSTR-1 is the statement of outward supplies and it feeds the recipient's ITC data. GSTR-3B is the summary return in which you declare liability, claim ITC and pay tax. Tax is not paid through GSTR-1.

Who must register under GST even if turnover is below the threshold?

Categories include persons making inter-State taxable supplies of goods (subject to exceptions), casual taxable persons, non-resident taxable persons, e-commerce operators and persons liable under reverse charge. Check the full list in your official text.

When is e-invoicing applicable?

It applies to registered persons notified by the Government whose aggregate turnover exceeds the notified limit, with some classes exempt. Since the limit has changed over time, use the figure in the text supplied for your attempt.

Can I claim refund under the inverted duty structure for services?

The Rule 89(5) formula includes ITC on input services along with inputs in Net ITC. ITC on capital goods is excluded. Refund applies to outward supplies of goods or services where the input tax rate is higher than the output rate, subject to notified exclusions and to the output not being nil-rated or fully exempt.

Is an e-way bill needed for every movement of goods?

No. It is required when the consignment value exceeds the prescribed limit, and some goods and situations are exempt. Check the Rules for the limit and exemptions.