How did a tax case linked to biryani restaurants uncover '₹70,000 crore billing scam' across India?

Tax fraud inquiry against three biryani chains in Hyderabad has led authorities to uncover alleged widespread manipulation in bills and undeclared revenue, potentially ₹70,000 crore, by restaurants across India. Probe led officials to a billing software that had 'bulk delete', 'post-generation modification' functions that allegedly helped thousands of restaurants to under-report turnover.