Green’s Dictionary of Slang

to lay down money on, to wager on; to write down notes.

1975		‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 58: Red Face pulled out four fivers and whacked them on the card.
2005		M.B. ‘Chopper’ Read Chopper 4 157: I told this la de da old toff to whack all his dough on Leilani on the nose.