"Disposición" is, as you say, often a withdrawal, but that clearly wouldn't make sense here, so I'm thinking it may relate to another, slightly different meaning, namely "drawdown."

In Mexico I've often come across the term "disposición" with regard to loan facilities, to refer to each "drawdown" of the funds by the borrower, which are then deposited into the borrower's bank account. So my best guess is that it means a deposit made as a result of a funds drawn down from a loan.

"Para ello, en este estudio se ha clasificado al crédito empresarial en dos categorías: crédito revolvente y crédito no revolvente o simple. El primero se refiere a líneas de crédito en las cuales un acreditado puede volver a disponer de esos recursos una vez que haya pagado parcial o totalmente el monto de la línea pactada. En el segundo tipo de crédito, las disposiciones están establecidas previamente, y pueden ser de una sola o varias disposiciones durante un periodo de tiempo, según lo estipule el contrato."
https://www.gob.mx/cms/uploads/attachment/file/71398/20_2012...

"In finance, the drawdown is a concept related to loan facilities that allow the borrower to obtain funds from a credit line during the loan period.

A drawdown refers to each of the amounts the borrower accesses from the loan facility."

https://www.kantox.com/en/glossary/drawdown/