Dear members,

I am a GST-registered marketplace seller (Karnataka). Each month the source data is marketplace sales + returns (Excel/CSV), not a Tally invoice book.

I have been preparing GSTR-1 offline JSON myself for portal upload (Prepare Offline). Typical issues in this data:

- B2CS state-wise net of returns
- Table 12 HSN bifurcated as hsn_b2b / hsn_b2c from May 2025 schema
- CGST = SGST after rounding on intra rows
- Table 13: invoice serials from marketplace (e.g. I2927NI…) vs credit-note series from books
- Returns with missing HSN needing to net against the original SKU/HSN
- Envelope version GST3.2.4, hash as per offline tool

I built a small Windows desktop utility for my own filing: upload the marketplace file, review orders, export Excel (B2B / B2C / HSN) and GSTR-1 JSON. Files stay on the PC; it does not log in to gst.gov.in.

I would value views from members who handle ecommerce clients:

1. Is Table 13 CN as a continuous books serial (not marketplace return IDs) the right practice?
2. Any GSTN JSON field you still see portal reject after 3.2.4 (HSN user_desc length, empty hsn_b2b, etc.)?
3. Would this be useful as a pre-processing step before the CA files, or do you already use Tally / other JSON tools for marketplace?

Happy to walk through a sample (dummy GSTIN) on a screen share. Not selling a filing service and I do not need client GST credentials.

Regards