You can still scan the code on BKK vehicles after boarding, but the surcharge will be more expensive from November.

BKK allows passengers to validate digital tickets after boarding using QR codes, but fines will increase from November. Passengers can scan codes inside vehicles if they couldn't validate before boarding. QR codes will be available on buses, trolleys, and trams. However, tickets must be validated immediately after boarding, as codes won't work during inspections. Starting November 2, fines will rise: on-site fines will increase from 12,000 HUF to 15,000 HUF, and fines paid within 30 days will rise from 25,000 HUF to 30,000 HUF. Discounted fines for monthly passes shown within two days will change from 6,000 HUF to 7,500 HUF.