The 3 GST invoice-numbering mistakes that will fail a pharmacy audit

GST rules on invoice serials look simple — unique, sequential, per financial year. In practice, three mistakes trip up almost every retailer we onboard.

Mistake 1: Resetting mid-year

If your billing software restarts the counter after a crash, a reinstall, or a "clean-up," you'll get two invoices with the same number. Any customer's CA who spots this on a 2A reconciliation will call it out. The fix isn't running gap-report macros in Excel — it's using a POS that stores the counter in the database, not on the machine.

Mistake 2: Cashier suffixes

"INV-0451-A" for Amit and "INV-0451-R" for Rohit is not a valid pattern. Serials must be unique on their own. Assign each cashier a device or a counter, not a suffix.

Mistake 3: Multi-outlet collisions

Chains with three outlets all running INV-0001 on 1 April are creating an audit nightmare. Either put each outlet on its own series (INV-KOR-0001, INV-JUB-0001) or make the counter strictly per-outlet in the database.

What good looks like

• Serials strictly monotonic per outlet, per financial year.
• No prefixes that change mid-year (INV → BILL is fine at year rollover, not on 15 October).
• Cancelled invoices leave the serial recorded as "cancelled" — you never re-use it.
• Credit notes are their own series, linked to the source invoice.