Invalid GSTIN of the recipient: the shapes a GSTIN takes, and what to do with a wrong one

A recipient GSTIN is refused when its shape or check digit is wrong, or the registration was not active. How to tell which, and what to do with the sale.

Why does the portal say a recipient’s GSTIN is invalid?

For one of three reasons, and they need different answers. The number is not in any shape GSTN issues, so it cannot be anyone’s: that is RET191113, "The GSTIN is invalid. Please enter a valid GSTIN." The number is well formed but its last character is not the check digit the first fourteen give, which is a typing fault; the offline tool’s manual says an invalid or wrong GSTIN comes back in the error report as "Enter valid GSTIN/UIN". Or the number is right and the registration was not active when you invoiced, which is RET191360, "GSTIN of receiver is inactive". GSTN’s FAQ on GSTR-1 says to upload invoice details only if the recipient was active on the date of issue.

Two more refusals name the buyer’s GSTIN without it being wrong. RET191314 is your own GSTIN in the buyer column; a business cannot supply itself under one registration. RET191316 is an invoice marked as a supply to an SEZ for a buyer whose registration is not an SEZ unit or developer.

The offline tool checks only the first kind. Its manual says it cannot tell whether a GSTIN is active or inactive, and shows an error only when the number is not in the standard format.

What are the fifteen characters?

An ordinary GSTIN is built from the business’s PAN. GSTN publishes the pattern of each kind of registration with its Returns APIs, and for a regular one it runs:

• •Two digits: the state code of the registration, 01 to 38, or 97 for Other Territory. 99, Centre Jurisdiction, opens a registration administered centrally, such as a foreign provider of online services. No registration begins 00, 39 to 95, 96 or 98.
• •Ten characters: the PAN, five letters, four digits and a letter. Every registration a business holds, in any state, carries the same ten.
• •One character: the entity number, a digit from 1 to 9 or a letter, which tells apart two registrations under one PAN in one state. It is never 0.
• •One character: Z, a digit from 1 to 9, or a letter from A to J in GSTN’s pattern for a normal registration. An e-commerce operator’s registration for collecting tax at source carries C here, and one for deducting tax at source carries D.
• •One character: the check digit, worked out from the first fourteen.

Which other shapes can a GSTIN take?

Not every registration has a PAN, and GSTN publishes a pattern for each that does not. A seller meets them rarely, but a validator that knows only the first shape calls a right number wrong:

• •A UN body or an embassy (a UIN): after the state code, two digits of year, a three-letter country code, a five-digit serial, UN or ON, and the check digit.
• •A non-resident taxable person: the same layout with NR in place of UN.
• •A foreign provider of online services (OIDAR): the same layout with OS, and always beginning 99.
• •A government department or office registered on its TAN, four letters, five digits and a letter, in place of a PAN; and a registration to deduct tax at source, which carries D in the fourteenth place.

How is the check digit worked out?

Each of the first fourteen characters is given a value: 0 to 9 for the digits, and 10 to 35 for A to Z. The values are multiplied in turn by 1 and 2, starting with 1. Each product is split into how many 36s it holds and what is left over, and both parts are added to a running total. The check digit is the character whose value is 36 less the total’s remainder by 36, or 0 when that remainder is 0.

The point of the rule is that one mistyped character always changes the check digit, so a number with a single slip in it fails. It does not prove the number was issued to anyone. The free GSTIN checker works the digit out and names the one it expected.

What should you do with the invoice?

First find out which of the three it was. Then:

• •A typing fault: ask the buyer for their GSTIN again, from their registration certificate or an invoice they have issued, and correct it in your register, not only in the JSON. The same buyer will be on next month’s invoices.
• •A number of the wrong shape that the buyer cannot correct: they may not be registered at all. A supply to a person who is not registered is reported as a sale to a consumer, in Table 7, or in Table 5 if it is inter-state and above the threshold.
• •A registration that was not active on the invoice date: the portal will not take the invoice in Table 4 against it. Report it as a sale to a consumer, and tell the buyer, who cannot take credit for it.
• •Your own GSTIN in the buyer column: find where your register or the marketplace report put it there. A transfer between two of your own registrations in different states has the other registration as the buyer, not this one.

What happens once the return is filed?

Before filing, a corrected JSON uploaded again replaces the invoice it carries, so this is the time to fix it. After filing, an invoice can be corrected only by an amendment in a later month’s return, and GSTN’s offline tool manual says the recipient’s GSTIN is one of the things an amended B2B invoice cannot change. Amending a GSTR-1 sets out what can be amended and until when.

Can a GSTIN pass one check and fail another?

No. The free GSTIN checker, the app and the JSON check all hold a number to the same shapes, the ones GSTN publishes with its Returns APIs: in the fourteenth place of a normal registration only Z, a digit from 1 to 9, or a letter from A to J, with C for an operator collecting tax at source and D for a deductor. A number with K to Y there is refused in all three places, as GSTN’s schema refuses it in a JSON. The check digit and the state code are the same in all three.

What does fynxIQ do with a buyer’s wrong GSTIN?

Every buyer GSTIN in the month is checked for its shape, its state code and its check digit before the return is built, in every shape GSTN publishes, the ones without a PAN included. An invoice whose buyer GSTIN fails is not guessed into Table 4. It is reported as a sale to a consumer, and a warning names it and the invoices it moved. Type the registration that was meant and it goes back to Table 4 with the buyer named; or say the buyer is a consumer and the warning closes. Your register is not changed either way.

Your own GSTIN as a buyer stops the download, because it can only be a mistake. What fynxIQ cannot know is whether a well-formed registration was active on the day. Its checks read the return alone, not the portal, so a cancelled buyer passes every check here; the Search Taxpayer page is where that is answered.

Where this comes from

• •GSTN, Returns API overview, the GSTIN patterns for each kind of registration (developer.gst.gov.in): the shapes of a normal, UN body, government, non-resident, TDS, TCS and OIDAR registration.
• •GSTN, request schema of GSTR1 - Save GSTR1 data, v4.1, and its error codes: the patterns a recipient’s GSTIN is held to; RET191113, RET191360, RET191314 and RET191316.
• •GSTN, FAQs on Form GSTR-1 (tutorial.gst.gov.in): invoice details accepted only if the recipient was active on the date of issue.
• •GSTN, Returns Offline Tool FAQs and user manual: the tool checks a GSTIN’s format, not whether it is active; an amended B2B invoice cannot change the recipient’s GSTIN.
• •CGST Act, section 25(9) and section 55: the unique identity number given to a UN body, an embassy and the like.
• •CGST Act, section 25(4): each registration of one PAN in another state is a distinct person, so a transfer between them has the other registration as its buyer.
• •fynxIQ’s engine: reference/gstin.ts, and the buyer GSTIN check in validate/rules.ts: the check digit, the state codes, the shapes, and what happens to an invoice whose buyer GSTIN fails.

Try it on your own figures with the free GSTIN checker.

Which file to download, and from where: the list for each marketplace and the GST portal.

By Raunak Pathak, founder of fynxIQ, who files GST returns on it. Last updated 4 October 2026. This is general information about how GST returns work, not advice about your particular return.