Most invoicing software demos show you a pretty PDF. That is the easy part. What determines whether a tool survives contact with Indian GST is far less photogenic: HSN codes on an item master, place-of-supply logic, IRN failure handling, and whether a closed period can be edited. Here is the checklist we use when scoping billing for a client.
First, Work Out Which Regime You Are In
Your obligations split at one number. E-invoicing is mandatory where aggregate annual turnover crossed Rs. 5 crore in any financial year from 2017-18 onwards; that threshold has applied since 1 August 2023. Under it, you issue ordinary GST tax invoices. Over it, every B2B invoice must be reported to an Invoice Registration Portal, which returns an IRN and a signed QR code — and an invoice without that IRN is not a valid document.
Two practical consequences. If you are below the threshold but growing, buy software that can switch on e-invoicing without a migration. If you are above it, your invoicing tool now has a hard dependency on an external API, which changes what "working" means.
The Eight Checks
1. HSN and SAC codes live on the item master
Not typed per invoice. The code determines the tax rate; if a human picks it each time, the rate becomes a typo risk on every line. Goods use HSN, services use SAC, and the number of digits required scales with turnover.
2. Place of supply is derived, not chosen
Intra-state supply means CGST plus SGST; inter-state means IGST. This follows from the parties' states and the nature of supply, so the software should compute it from the client's registered address and let you override only with a reason. Tools that present it as a dropdown produce wrong invoices at scale.
3. Invoice numbering is sequential, gapless and per financial year
GST requires a consecutive series. If your software lets a user delete invoice 47, you now have a gap you must explain. Deletion should be impossible; cancellation and credit notes are the correct mechanisms.
4. IRN failures are queued, not dropped
The IRP will be unavailable sometimes. The right behaviour is a persistent queue with visible status per invoice and automatic retry; the wrong behaviour is an error toast and a lost document. Ask a vendor directly what happens when the portal is down — the answer tells you how seriously the integration was built.
5. Credit notes and debit notes are first-class
Partial returns, rate corrections and post-supply discounts all need a linked note referencing the original invoice, because that linkage is what makes your GSTR-1 reconcile.
6. GSTR-1 export matches the portal's current format
A JSON or Excel export that the GST portal actually accepts this quarter. Formats change; a tool whose export was correct two years ago is not automatically correct now.
7. E-way bill generation is in the same flow
If you ship goods above the state's consignment value threshold, generating the e-way bill from the same invoice record rather than re-keying it on a separate portal removes an entire class of mismatch.
8. Your data leaves cleanly
Full export of invoices, clients, items and payments in a structured format, on demand, without a support ticket. Invoice history is the one dataset you legally must retain and the one vendors most often make sticky.
The Collections Problem Nobody Puts in the Demo
Generating an invoice is a five-minute job. Getting paid is the actual work, and it is where standalone billing tools go quiet. What changes outcomes:
- Ageing by client, not by invoice. "Who owes us money and for how long" is the question; a list of overdue invoices is not the same answer.
- Automated reminders with a human escape hatch. Scheduled nudges at day 7, 15 and 30, which stop the moment the account owner intervenes. WhatsApp utility messages are cheap for this — roughly Rs. 0.11 to Rs. 0.13 per delivered message at current India list rates — but they must be template-approved and consent-based.
- Payment status visible to the person who owns the relationship. If only accounts can see that a client is 45 days late, the one person who could pick up the phone does not know.
This is the structural argument for invoicing inside your CRM rather than beside it: the client record already knows who owns the relationship.
Where Free Tiers Make Sense
Under roughly 30 invoices a month, with no e-invoicing obligation and domestic clients only, a free tool is the correct answer and anything else is overspending. Re-evaluate when any of three things happen: you approach the turnover threshold, you start shipping goods interstate, or collections stop fitting in one person's head.
Conclusion
Judge GST invoicing software on the boring surfaces — item master, numbering, place-of-supply logic, IRN retry, export. The PDF template is the part you will think about least after week one.
If you want a second opinion on whether your billing should sit inside your CRM or stay separate, describe your setup to us and we will tell you plainly. Treat everything above as a starting checklist, not tax advice — confirm thresholds and formats with your CA.
Frequently Asked Questions
Is e-invoicing mandatory for my business?
E-invoicing under GST is mandatory for businesses whose aggregate annual turnover crossed Rs. 5 crore in any financial year from 2017-18 onwards — a threshold in force since 1 August 2023 and unchanged as of 2026. Below that you issue normal GST tax invoices with no IRN. Thresholds have been reduced in stages before, so confirm the current figure on the GST portal or with your CA rather than trusting a vendor's landing page.
What is the difference between a GST invoice and an e-invoice?
A GST invoice is a document you generate yourself with the prescribed fields. An e-invoice is that same document after it has been reported to an Invoice Registration Portal, which returns an Invoice Reference Number (IRN) and a signed QR code. The invoice is only legally valid as an e-invoice once the IRN exists, so software that cannot reach the IRP leaves you unable to bill.
Does free GST billing software exist and is it safe to use?
Free tiers exist and are fine for low volumes, with two caveats. Check whether your data is exportable in a complete, structured format, because invoice history is the hardest thing to recover later. And check whether e-invoicing and e-way bill generation sit behind a paid tier — if you are near the turnover threshold, that is a bill you will meet at the worst possible moment.
Can invoicing live inside my CRM instead of a separate tool?
It should, if your billing follows your sales. The reason is data lineage: a won deal becomes a client, the client gets a project, the project gets invoiced, and payment status feeds back to the account owner. Separate tools break that chain and turn collections into manual follow-up. BlazeCRM is built this way deliberately.
What happens if I enter the wrong HSN code?
The wrong HSN usually means the wrong tax rate, which means a short payment or over-collection of GST and a mismatch in GSTR-1. Correcting it needs a credit note and a fresh invoice, not an edit. Good software stores the HSN against the item master so the code is chosen once rather than retyped per invoice.