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GSTIN validation
A customer's GSTIN — their 15-character GST registration number — is what tells GST Manager to treat them as a business (B2B) rather than a consumer (B2C). This guide shows where that number is captured, how it's validated, and what it changes on the invoice.
B2B vs B2C
A customer with a valid GSTIN is B2B; a customer without one is B2C. The distinction drives classification and appears as a separate section in your GSTR-1 report.
Where the GSTIN is captured
Your customer enters their GSTIN on the AcelleMail contact page, in their Tax ID field. The field carries the hint "Enter your 15-character GSTIN to receive GST tax invoices." so customers know why it's worth filling in, plus a format hint: "Format: 22AAAAA0000A1Z5 — state code + PAN + entity + Z + check digit."
AcelleMail → Contact → Tax ID
How the number is validated
GST Manager checks the GSTIN as it's entered. A valid number is 15 characters and breaks down as 22AAAAA0000A1Z5:
- State code — the leading two digits identify the state.
- PAN — the embedded 10-character PAN of the registered entity.
- Entity and Z — the entity code followed by a fixed
Z. - Check digit — the final character, verified against the rest.
When the format, state code, embedded PAN and check digit all pass, you see "GSTIN format is valid." If any part fails, you see "GSTIN is invalid." — correct the number before relying on it.
What a valid GSTIN changes
Once a customer has a valid GSTIN on file, their invoices are classified B2B; without one, they stay B2C. Combined with the customer's state and your home state, this decides whether tax splits into CGST + SGST or a single IGST line — see GST classification for the full logic. Make sure your own Company GSTIN and home state are set first, in Configure GST.