Select the most appropriate idiom to fill in the blank.

Due to an unexpected increase in operational costs and reduced revenue, the local non-profit had to ____________ to avoid shutting down entirely.

The correct option is tighten its belt.

Explanation of the correct idiom:
The idiom "tighten its belt" means to cut back on spending, reduce expenses, or live more frugally due to financial strain. In the context of the sentence, the local non-profit is dealing with an unexpected increase in operational costs and reduced revenue. Therefore, cutting back on spending is the appropriate measure to prevent shutting down.

Meanings of the other options:
• Spill the beans: To reveal confidential or secret information.
• Bark up the wrong tree: To pursue a mistaken course of action or direct one's efforts toward the wrong target.
• Face the music: To accept the unpleasant consequences or punishment for one's actions.