Go to the System Administration menu -> Control File Maintenance Menu -> System Parameters Menu -> Define Site Control Parameters (LG0144).
There are two ways you can do this:
Option 1: Click the 'A/P' button (LG0541) and mark 'Place Invoice on Hold for Insufficient Funds'.
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Option 2: Click on the 'Budget Ctrl' button (LG0587) and uncheck where it says 'Allow Over Expend'.
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