---
url: /gst-manager-acellemail/guides/gstin-validation.md
description: >-
  How customer GSTINs are captured on the AcelleMail contact page, how GST
  Manager validates the 15-character format, and how a valid GSTIN switches an
  invoice between B2B and B2C.
---

# 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.

::: info 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](/gst-manager-acellemail/img/gst-gstin-validation-taxid.png)
*AcelleMail → Contact → Tax ID*

## Format validation structure

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:

* **Valid input:** Displays confirmation message *"GSTIN format is valid."*
* **Invalid input:** Displays warning message *"GSTIN is invalid."*

## Invoice classification outcomes

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](/gst-manager-acellemail/guides/configure-gst).

## Related pages

* [GST classification](/gst-manager-acellemail/features/gst-classification) — tax determination engine
* [Configure GST](/gst-manager-acellemail/guides/configure-gst) — merchant GSTIN configuration
* [Tax reports](/gst-manager-acellemail/features/tax-reports) — B2B and B2C export data