An invoice is held back
Open checks.csv; fix the line it names (GSTIN, rate, invoice number or date) and run again.
IGST shown for a local buyer
Check the place of supply column; leave it blank to use the buyer GSTIN's state.
Error: seller details GSTIN
Your GSTIN has a typo; the check digit does not match. Copy it from your GST certificate.
Formulas show as text in Google Sheets
Import with File > Import > Upload, not by pasting cells.
Claude does not use the skill
Check it is switched on in Settings → Capabilities → Skills, then name it in your message.
The script says a column is missing
Rename your header to one of the names in README, or say the mapping in your message.
Code execution is off
Skills with scripts need code execution enabled in Claude.ai settings.
FAQ
How does it decide CGST + SGST or IGST? From the state codes: your GSTIN's first two digits versus the place of supply. Same state means CGST + SGST (or UTGST); different means IGST.
Can I use it without Claude or Python? Yes. Open samples/gst-invoice-template.xlsx in Excel or Google Sheets. The tax split and totals are formulas.
Does it make e-invoices? No. It makes regular tax invoices. If your turnover requires e-invoicing, generate the IRN on the government portal.
Is it really free? Yes, free forever, no account and no cap besides 500 invoices per run.