knock in, v.¹ — Green’s Dictionary of Slang

knock in v.¹

[the money is ‘knocked in’ to the coster’s pocket]

(costermonger) to make money.

1877		J. Diprose London Life 42: These knights of the barrow – in the language of the fraternity – often boast that if one ‘pulls up his boot,’ he can ‘make the up his leg’ by going to market early and ‘knock in’ his ‘ten or twelve hog afore breakfast’.
1909		J. Ware Passing Eng. of the Victorian Era.