Green’s Dictionary of Slang

(US) a wealthy person who will usu. pay the bill in a restaurant/bar etc.

1922		Ogden Standard Examiner 12 Apr. 6/5: We crashed in at the Plaza. A friend of Harry’s we met there was the darbs.
1922		Appleton Post-Crescent (WI) 2 May 9/4: Flapper Dictionary darbs – A person with money who can be relied on to pay the check.