Yes, you can indeed use cash to pay for your fare on most standard franchised double-decker buses and green minibuses operating throughout Hong Kong, but there is a strict condition regarding the exact amount. Public buses do not issue change to passengers under any circumstances. If your specific journey fare requires a certain amount and you deposit a larger coin or banknote, you will effectively forfeit the excess balance as no refund or change ticket will be given by the driver or the fare box. Because of this strict exact-fare policy, most local commuters and visitors prefer utilizing electronic options like the Octopus card or contactless digital payments to ensure smooth travel without worrying about coin denominations.