Pony up is an idiom meaning to pay what you owe or settle your debt.
It is also used as “to put money up” for something to provide the necessary funds for something.
The idiom dates back to the 16th century and is said to be a corruption of “legem pone”, the first two words of Psalm 119 that was sung on English quarter day, when debts were settled and payments were made.
The term became associated with payments and hence was used as an expression for “cash down”.
Its meaning was first recorded by Thomas Tusser in Hundreth Good Pointes Husbandry in 1570: “Use Legem pone to pay at thy day”.
The term “pony up” itself was first used in print in a Connecticut publication The Rural Magazine in 1819.
Interestingly, despite its English origin, it is known to be an American phrase.
The term has been regularly used since the early 19th century in spoken language as well as in publications, but it has become popular since 1980.
The first posts of “pony up” were published on Urban Dictionary in 2004.