“In the money”

“In the money” means that a money prize has been won. For example, a horse that finishes a race first (“win”), second (“place”) or third (“show”) finishes “in the money.” The term “in the money” has been used in horse racing since at least 1895. The term was further popularized by the 1933 song hit, “We’re in the money.”
 
“On the money” means “accurately” or “precisely” and has been cited in print since at least 1939.
   
 
(Oxford English Dictionary)
in the money: finishing among the winners in a competitive event, esp. a horse race (cf. sense 2e); (more generally) (in the position of) possessing adequate or substantial money or wealth; wealthy, successful.
1902 ‘D. Dix’ Fables of Elite 48   It is True that when the Spurt is over I am generally in the Money.
1926 L. Hughes Let. 20 Jan. in L. Hughes & C. Van Vechten Remember me to Harlem (2001) 36   Her only comment on the art of the Blues was that they had put her ‘in de money’.
1928 Morning Post 20 Oct. 6/1   One of them is to-day a full champion, the other three all winners, and ‘in the money’, as the fanciers say, whenever shown.
 
30 November 1895, The State (Columbia, SC), “On the Turf,” pg. 1, col. 5:
The last race proved a big dump for the talent, as none of the choices finished in the money.
 
1 January 1897, Cleveland (OH) Leader, “Pedestrianism,” pg. 3, col. 2:
Earl is surprising every one by his gameness and speed, and he will probably finish in the money.
 
Daily Racing Form Archives
24 July 1897, Daily Racing Form, pg. 3, col. 1:
King Galong seemed to have a chance to be in the money at the head of the stretch but collapsed.
 
OCLC WorldCat record
The gold diggers’ song : we’re in the money
Author: Harry Warren; Al Dubin; Richard L Halle
Publisher: [S.l.] : M. Witmark & Sons, 1933.
Edition/Format:  Musical score : Songs : No Linguistic Content