A discount on the bill is a decision with a name on it
The folio's fourth tab: a percentage or an amount off the whole bill, the room, the food or one line, the GST reduced with it, a reason from the hotel's list and a name on every line — a manager above the hotel's limit. And a small leftover forgiven at the door, under a ceiling, recorded.
A reduction that cannot be recorded is recorded as something else — a short till, a payment that never happened, a void of a charge that was right. The restaurant has had a proper discount since its till was built; the room bill now has the same.
On the bill
The whole bill, the room, food and beverage, everything else, or one line; a percentage or a rupee amount; the reason from the hotel's own list; approved by yourself up to the hotel's limit and by a manager above it. It lands as an allowance per tax slab with the reason and the name on every line and on the booking's history, and the GST comes back with it — a discount shown on the invoice before it is issued reduces the value of supply, and the return files what the invoice printed. The room's slab is not re-read. A price for the nights still to come is a rate change, not a discount, and the tab says so.
At the door
A guest owes ₹150 and has their bags in hand. Up to the hotel's ceiling — ₹500 unless changed — the desk waives it at check-out with a reason, as an allowance against their name; above it, a manager. No tax is touched: a goodwill reduction after the supply is the hotel's cost. A bill in credit is the opposite question, retain or refund, asked in the same click.
The limits are the hotel's
Both ceilings are on the hotel's details, set by the account administrator: the rupees the desk may waive, the share of a bill the desk may discount. A hotel that wants a manager for every rupee leaves them at zero; that is a row, not a release.