What should an advertiser do if the sum of projected spend across line items is less than the total lifetime order budget?

The correct answer is Open up line items targeting settings or increase maximum average CPM because if the sum of projected spend across line items is less than the total lifetime order budget, the advertiser needs to adjust settings to ensure the full budget is spent efficiently. By opening up line item targeting settings, the advertiser can broaden the audience or reach additional impressions, increasing the likelihood of full budget utilization. Alternatively, increasing the maximum average CPM can make the campaign more competitive in the auction, helping to secure more impressions and drive more spend. These adjustments ensure that the campaign delivers the desired results without underdelivering. Simply doing nothing or decreasing the campaign budget would not address the issue of underdelivering and would reduce the campaign's potential effectiveness.