The Free Dictionary
the ghost walks
An expression used in theater to explain that actors will perform because they have been assured of payment. The phrase possibly originated when an actor playing Hamlet’s father (who appears in Hamlet as a ghost) refused to act unless he was paid.
The ghost walks today because we all just got paid!
 
(Oxford English Dictionary)
ghost, n. and adj.
Originally Theatre slang. the ghost walks and variants: salaries are paid.
1831   Atlas 29 May 358/3   On Saturday the actors at Drury Lane were struck with horror to find that no ‘ghost walked’; that is, that the treasury was shut.
1833   R. Dyer Nine Years Actor’s Life 53   If I played with applause, it was a matter of indifference whether ‘the ghost’ walked on Saturday or not.
1883   Referee 24 June 3/2   An Actor’s Benevolent Fund box placed on the treasurer’s desk every day when the ghost walks would get many an odd shilling or sixpence put into it.
1952   Rushville (Indiana) Republican 1 Aug. 6/2   There is always one day when no one on the office staff calls in sick. That is the day the ghost walks—payday.
   
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Dickens Journals Online
October 1853, Household Words (a weekly journal conducted by Charles Dickens), “Slang,” pg. 77, col. 1:
And the Stage has its slang, both before and behind the curtain. Actors speak of such and such a farce being a “screamer,” and such and such a tragedy being “damned” or “goosed.” If an actor forgets his part while on the stage, he is said to “stick ” and to “corpse ” the actors who may be performing with him, by putting them out in their parts. A “part” has so many “lengths;” a piece will “run ” so many nights. Belville is going in the country to “star ” it. When no salaries are forthcoming on Saturday, the “ghost doesn’t walk”—a benefit is a “ben,” a salary a “sal;” an actor is not engaged to play tragedy or comedy, but to “do the heavy business,” or “second low comedy,” and when he is out of an engagement he is said to be “out of collar.”
 
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HerDiaz
@Hernandiaz2005
“The Ghost Walks”
Theater slang for getting paid. Meant to sarcastically convey the rarity of the event “When Hell freezes over” expression.
11:14 PM · Jan 11, 2013
 
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Paula Becker
@PaulaBeckerNow
#Theater #Slang Ghost: The treasurer of a show company. When the actors are paid, the ghost walks.
7:15 PM · Apr 19, 2014
 
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Wunderkammer
@DirkPuehl
“For which they say you Spirites oft walke in death” (Shakespeare)
Theatres are famously full of them. But when “the ghost walks,” British actors got paid, after one, in 1831 in Drury Lane, refused to go on stage as Hamlet’s father until accounts were settled
#SuperstitionSat
12:20 PM · Dec 10, 2022