The ₹3.6 Lakh Mistake: When Priya Charged the Wrong GST on an Inter-State Invoice

Priya runs a small branding studio in Pune. Six people, mostly young designers, with a healthy mix of clients across Maharashtra and a few outside the state. Her GST filing was always on time. So when her accountant called in a panic one afternoon, she was genuinely confused. The problem wasn't a missed return. It was a single wrong tax head on one invoice.

The invoice that looked perfect

In April, Priya's studio completed a logo and packaging project for a client in Bengaluru. The fee was ₹20,00,000. She raised a tax invoice at 18% GST, which came to ₹3,60,000 in tax. The invoice looked clean and professional.

The mistake was in how that ₹3,60,000 was split. Priya's software defaulted to her home state settings, so it charged:

• CGST at 9% = ₹1,80,000
• SGST at 9% = ₹1,80,000

That is the correct split for an intra-state supply. But this was an inter-state supply: her studio in Maharashtra supplying a client in Karnataka. For services, the place of supply here is the client's location. Inter-state supplies attract a single IGST at 18% = ₹3,60,000, not CGST + SGST.

The total tax amount was identical. So why did it matter?

Why the client refused to pay

The Bengaluru client's accounts team caught it during their GSTR-2B reconciliation. Their argument was simple and correct: a Karnataka business cannot claim Maharashtra SGST as input tax credit. The credit she had passed on was, for them, unusable.

They held back payment of the tax portion until the invoice was corrected. For Priya, ₹3,60,000 was suddenly stuck.

The part that hurts: you can't just "swap" the heads

Here is what many small businesses don't realise. Once you've reported and paid CGST + SGST in your GSTR-3B, you cannot simply move that money to the IGST head. The law treats wrong-head payment as tax paid under the wrong category. The practical fix usually means:

1. Issue a credit note against the original wrong invoice (or correct it through an amendment, depending on timing and whether payment was settled).
2. Raise a fresh invoice with the correct IGST head so the client can claim ITC.
3. Pay IGST for the period in which the correct invoice falls.
4. Claim a refund of the wrongly paid CGST + SGST, or adjust it going forward.

The refund route is where the cash-flow pain shows up. For a stretch of time, Priya had effectively paid the tax twice: ₹3,60,000 as CGST + SGST already in the system, and a fresh ₹3,60,000 as IGST. The refund for the wrong head takes its own sweet time and paperwork.

There is relief in the law for tax paid under the wrong head — it isn't treated as a permanent loss, and interest treatment is meant to be lenient when the correct tax is later paid. But the working-capital hit and the back-and-forth with the department were very real for a six-person studio.

What Priya changed afterwards

The fix wasn't dramatic. It was discipline.

• Set place of supply per client, not per home state. Her billing tool now flags inter-state versus intra-state automatically based on the client's GSTIN state code.
• Check the first two digits of the client's GSTIN. Those represent the state. If they don't match her own state code, it's IGST.
• Reconcile before filing GSTR-1. A quick check of tax heads catches this in minutes, not months.

The lesson

The total GST collected was never wrong. Priya didn't underpay the government by a single rupee. And yet one mis-set default cost her months of follow-up, a strained client relationship, and a temporary ₹3.6 lakh hole in her cash flow.

GST isn't only about paying the right amount. It's about paying it under the right head, so the credit chain stays unbroken for everyone down the line. For service businesses billing across states, the question to ask on every invoice is the simplest one: where is my customer? Answer that correctly, and the tax heads sort themselves out.