Debt is a game mechanic in Bloons TD 6 and Bloons TD Battles 2. It causes all cash the player earns to be reduced by 50% until their debt is fully paid off. Debt is displayed in red text with a minus sign behind the dollar sign. In Co-op, debt is separate for each player, and it only affects players that have debt.
This section needs more screenshots. See the screenshot guidelines for more information on what screenshots are needed and how to add them. The editor that added this notice elaborates: Debt in Battles 2