In Hindi: कच्चा बिल / पक्का बिल · Also called: kacha bill, rough bill
Shops use the two words for two kinds of paper. A kaccha bill is informal: a rough estimate, a quotation, a list of what the customer is taking with prices written in, often on a plain pad with no number and no tax. A pakka bill is the real thing: a numbered invoice with the shop's details, the one that stands as the record of the sale.
For a GST-registered shop the difference is not a matter of style. The law asks for a tax invoice (or, in some cases, a bill of supply) when goods are removed or delivered. A kaccha bill is neither, so a sale made on one alone has no invoice behind it.
Kaccha bills still have an honest use: a price given before the customer decides, or an order taken before the goods arrive.
