Reverse charge on a scanned purchase. OCR must not invent the tax.

You buy raw material from a transporter who is not GST-registered. The invoice carries a total: ₹18,000 for freight. No GST. No CGST, no SGST. Under reverse charge, you are liable to pay the tax. The supplier is not. The photocopy arrives with blank tax columns. A vision model has seen ten thousand regular invoices with filled tax columns. It fills in 18%. The total closes. The books say you owe ₹18,000 plus ₹3,240 of CGST and SGST. The reality is different: you owe ₹3,240 in tax to the government, not to the supplier. The supplier does not collect it.

Reverse charge is a GST mechanism where the recipient pays the tax instead of the supplier. It applies to specific categories: goods and services notified under Section 9(3), imports, and supplies from unregistered persons under Section 9(4) (within the thresholds and categories the Act and notifications specify). Read CBIC for the current list. I will not paste a frozen table here as if it were eternal law. Categories change. Thresholds change.

The OCR trap is the same as composition

See composition invoices. The trap is identical: blank tax columns, a model that fills them, a total that closes on fiction. The difference is ITC treatment. Composition: no credit. RCM: credit if you self-pay and the Act permits. Those are different CA decisions. We do not make either of them.

The gate catches both the same way: required fields. If tax is blank on a line that should carry tax, the row needs a person. If the model invents tax that closes, the row may pass the gate. That is a process risk, not a product feature. Pin known RCM vendors the way you pin composition vendors.

What the clerk should do

See a bill with no GST columns and a total that looks like goods plus freight: do not fill in tax. Check the supplier on the GST portal. If unregistered, the tax treatment is RCM. Park the row. Let the CA confirm the ITC treatment under Section 16. Link section 16.

If the supplier is registered but the invoice omits tax because they issued a composition bill, that is composition, not RCM. Different treatment. Same blank columns. Portal is the tie-break.

Do not paste a GSTIN onto an unregistered supplier's invoice so the row exports. That is how you fabricate a tax trail that does not exist. Required GSTIN exists so unregistered suppliers fail auto-export. That is the correct failure.

Tally

RCM purchases may need different ledgers than regular purchases. Tally Help and your CA for the correct treatment. We export the fields we extracted. We do not invent RCM-specific Tally groups. If the paper says "reverse charge" in a stamp, the clerk should see that in review. The factory face of RCM is freight: the missing tax that stares back at you.

Bake-off

Give the vendor a bill from an unregistered supplier: no GSTIN, total but no tax. If it auto-exports, that is a required-field failure that did not fire. If it goes to review, the gate worked. Do not fill in the missing tax to "see what the product does." That is how you fund the fiction.