GSTIN validation

A customer's Goods and Services Tax Identification Number (GSTIN) determines tax classification:

B2B transactions: Applied when a customer provides a validated 15-character GSTIN.
B2C transactions: Applied when no valid GSTIN is present on the customer account.
Reporting impact: Determines whether transactions map to B2B or B2C tables in GSTR-1 returns.

Classification summary

Valid GSTIN provided: Classified as B2B with input tax credit eligibility.
No GSTIN provided: Classified as B2C consumer sales.

Where the GSTIN is captured

Customers enter their tax identifier during account onboarding or profile updates:

Location: AcelleMail Contact profile in the Tax ID field.
Form guidance: Displays "Enter your 15-character GSTIN to receive GST tax invoices."
Format hint: Displays "Format: 22AAAAA0000A1Z5 — state code + PAN + entity + Z + check digit."

The Tax ID field on the AcelleMail contact page AcelleMail → Contact → Tax ID

Every GSTIN must conform to standard statutory formatting:

Segment	Structure	Purpose
State code	2 Digits	Identifies the registration state or union territory.
PAN	10 Characters	Embedded permanent account number of the entity.
Entity code	1 Alphanumeric	Registration count for the PAN within the state.
Default char	`Z`	Fixed statutory character.
Check digit	1 Alphanumeric	Mod-36 checksum character over prior 14 characters.

The validation engine provides immediate visual feedback:

A valid GSTIN triggers automated billing adjustments:

Invoice classification: Upgrades transaction from B2C to B2B.
Tax component split: Applies CGST + SGST (intra-state) or IGST (inter-state) based on merchant and customer state.
PDF rendering: Displays customer GSTIN and state code on downloaded tax invoices.

To configure your merchant identification, see Configure GST.