A wrong GSTIN on an invoice means your buyer cannot claim the input tax credit — and they will ask you to fix it. Most wrong GSTINs are typing mistakes, and most typing mistakes can be caught before the invoice is issued.
The 15 characters
Take a GSTIN like 08ABCDE1234F1Z5:
| Characters | Meaning |
|---|---|
| 1–2 | State code — 08 is Rajasthan |
| 3–12 | The holder’s PAN |
| 13 | Entity number — how many registrations this PAN has in the state (1–9, then A–Z) |
| 14 | Z by default |
| 15 | Check character, calculated from the first 14 |
The check character
The last character is computed from the other fourteen. If any one of them is mistyped, the check almost always fails. That is why a good billing app can tell you a GSTIN is wrong before you look it up — no internet needed.
What it cannot tell you is whether the GSTIN is active or belongs to the business you think it does.
Verifying on the GST portal
Use Search Taxpayer on the GST portal (no login needed) to see:
- the legal and trade name,
- whether the registration is active, suspended or cancelled,
- the principal place of business.
Check this for any new business customer, especially before a large credit sale.
In Billyng
Billyng checks a GSTIN’s length, shape and check character as it is entered, and says exactly what is wrong — “A GSTIN is 15 characters — this has 14” rather than “invalid”. The state code it carries is what decides whether a sale is charged CGST + SGST or IGST.