The GST department issued over 2.5 lakh notices in the last fiscal year for mismatches and errors in returns. Most of these notices were avoidable — caused not by fraud but by simple mistakes in data entry, classification, and filing.
If you are a business owner or a CA, these are the seven mistakes you are most likely making right now. Each one has a straightforward fix.
1. Wrong GSTIN on Invoices
The Problem: A single wrong digit in the buyer’s GSTIN makes the invoice invalid for their ITC claim. The buyer files a return claiming credit, but the GSTIN does not match, and the credit is rejected.
Why It Happens:
- Typing GSTIN manually instead of copy-pasting
- Not verifying the GSTIN before creating the invoice
- Using an old GSTIN (business changed registration)
How to Avoid:
- Always verify GSTIN using the GST portal’s “Search Taxpayer” feature
- Store verified GSTINs in your party master — do not re-enter each time
- Software that validates GSTIN format (15 characters, state code check digit) catches typos at entry
The Fix in Hisaabo: Party GSTINs are stored once and validated on save. Every invoice uses the stored, verified GSTIN — no manual re-entry.
2. Wrong Tax Type (CGST/SGST vs IGST)
The Problem: Charging CGST+SGST on an inter-state sale (should be IGST), or charging IGST on an intra-state sale (should be CGST+SGST). This happens when the business does not correctly determine the place of supply.
Why It Happens:
- Branch offices shipping from a different state than registered
- E-commerce sales where the marketplace reports the supply
- Service providers serving clients in multiple states
- Not updating the system when a client moves or registers in a different state
How to Avoid:
- Determine place of supply for every transaction
- If supplier state = recipient state → CGST + SGST
- If supplier state ≠ recipient state → IGST
- Use software that applies the correct tax type based on party state
The Fix in Hisaabo: The system compares your business state with the party’s state. The correct tax type is applied automatically. You cannot accidentally charge the wrong tax type.
3. Claiming Ineligible ITC
The Problem: Claiming Input Tax Credit on expenses that are not eligible under Section 17(5) of the CGST Act. Common ineligible items include:
- Motor vehicles (with exceptions)
- Food and beverages
- Health and fitness
- Travel and tour
- Cosmetic surgery
- Construction of immovable property
Why It Happens:
- Not knowing the blocked categories
- Recording all purchase invoices as ITC-eligible without review
- Not separating business and personal expenses
How to Avoid:
- Maintain a list of blocked ITC categories
- Review every purchase invoice for eligibility before claiming
- Record ineligible ITC separately in your books
The Fix in Hisaabo: Purchase invoices can be tagged as ITC-eligible or ineligible at the time of entry. The GSTR-3B report only includes eligible ITC.
4. Missing the GSTR-2B Reconciliation
The Problem: You claim ITC based on purchase invoices, but your supplier has not filed GSTR-1. Since ITC is auto-populated from GSTR-2B (which is based on supplier filings), your claim gets rejected.
Why It Happens:
- You recorded the purchase and claimed ITC
- Your supplier filed GSTR-1 late or not at all
- Your ITC claim exceeds what shows in GSTR-2B
- The GST system sends a notice for excess ITC
How to Avoid:
- Check GSTR-2B before filing GSTR-3B every month
- Match your purchase register against GSTR-2B
- Follow up with suppliers who have not filed
- Only claim ITC that appears in GSTR-2B
The Fix in Hisaabo: ITC matching is done continuously. When you record a purchase invoice, the system tracks whether the corresponding supplier filing exists. Before GSTR-3B filing, you get a clear report of eligible vs. pending ITC.
5. Invoice Number Gaps
The Problem: Invoice numbers should be sequential within a financial year. Gaps (INV-001, INV-002, INV-005) suggest unreported sales and invite scrutiny during audits.
Why It Happens:
- Manual invoice numbering with errors
- Deleting invoices creates gaps
- Different staff using different series
- Software that allows non-sequential numbers
How to Avoid:
- Use software that auto-generates sequential invoice numbers
- Never delete invoices — issue credit notes instead
- Use a single series per financial year
- If you must cancel, keep the number and mark it cancelled
The Fix in Hisaabo: Invoice numbers are generated atomically using database transactions. No gaps, no duplicates, even with concurrent users. Cancelled invoices are marked, not deleted.
6. Incorrect HSN/SAC Codes
The Problem: Every invoice must include HSN (goods) or SAC (services) codes. Wrong codes mean wrong tax rates, which affects both your liability and the buyer’s ITC.
Why It Happens:
- Looking up HSN codes manually for every invoice
- Using generic codes instead of specific ones
- Not updating codes when products change
- Confusion between similar products with different codes
How to Avoid:
- Assign HSN/SAC codes at the item level (once, not per invoice)
- Use the GST portal’s HSN search to verify codes
- Review your item master periodically for accuracy
The Fix in Hisaabo: HSN/SAC codes are stored per item. Once set, they appear on every invoice automatically. You set it once; it flows through to invoices, GSTR-1, and HSN summaries.
7. Not Filing Returns on Time
The Problem: Late filing attracts a penalty of Rs. 50/day (Rs. 20/day for nil returns) plus interest on tax liability at 18% per annum. Over a year, this adds up to significant avoidable cost.
Why It Happens:
- Data is not ready by the due date
- Waiting for client information
- Manual compilation of return data
- Procrastination (the deadline feels far until it is not)
How to Avoid:
- Maintain books throughout the month, not just at filing time
- Generate return data from your accounting system (not manual compilation)
- Set internal deadlines: GSTR-1 by the 9th, GSTR-3B by the 18th (buffer before actual deadline)
- Use a system where GST data is always ready
The Fix in Hisaabo: GSTR-1 and GSTR-3B reports are generated from your live data at any time. There is no “preparation” phase — the data is structured correctly from the moment you create an invoice.
Summary: Prevention Over Correction
| Mistake | Root Cause | Prevention |
|---|---|---|
| Wrong GSTIN | Manual entry | Store verified GSTINs in party master |
| Wrong tax type | Manual decision | Auto-apply based on party state |
| Ineligible ITC | No review process | Tag invoices at entry |
| Missing GSTR-2B match | No reconciliation | Continuous ITC matching |
| Invoice number gaps | Manual numbering | Auto-generate sequential numbers |
| Wrong HSN codes | Per-invoice lookup | Store per item, reuse automatically |
| Late filing | Data not ready | Maintain books continuously |
Every mistake on this list has the same root cause: manual processes on unstructured data. When your financial system enforces correct data at the point of entry, these errors become impossible.
Frequently Asked Questions
What should I do if I already made one of these mistakes?
File a correction in the current period’s return (GSTR-1 corrections go in the next period). For GSTR-3B, pay any additional liability with interest. For ITC wrongly claimed, reverse it voluntarily before the department sends a notice.
Will the GST department really send a notice for small errors?
Yes. The GST system auto-generates notices for ITC mismatches and GSTR-1/3B discrepancies. There is no minimum threshold.
How long do I have to correct GST errors?
GSTR-1 cannot be revised — corrections go in the next period. For annual return (GSTR-9), corrections can be made up to the filing deadline.
Is accounting software really necessary?
If you file GST, yes. Manual processes cannot enforce the data quality that GST compliance requires. The cost of software is far less than the cost of notices, penalties, and the CA’s time fixing errors.
Every GST mistake is preventable. The question is whether you prevent it at the source (correct data entry) or discover it at the destination (filing time). The first approach takes minutes. The second takes days.