When using campaign budget optimization (CBO), where should the budget be set: campaign level, ad set level, or both?

When using Campaign Budget Optimization (CBO), the budget should be set at the campaign level. CBO is a feature in Facebook Ads Manager that allows Facebook's algorithm to automatically distribute the campaign budget across ad sets in real-time to get the best results. If CBO is enabled, you should not set individual budgets at the ad set level. Instead, Facebook will dynamically allocate the budget to the ad sets that are performing best, optimizing for the chosen campaign objective. For example, if you have three ad sets targeting different audiences, and CBO is enabled with a $100 daily budget at the campaign level, Facebook might spend $60 on the ad set that's generating the most conversions, $30 on another, and $10 on the third, based on their respective performance.