You're reviewing impressions for a Programmatic Guaranteed deal in Display & Video 360 that you launched last week and notice that it under-delivered. What should you do first to learn why that happened?

The Deal Troubleshooter in Display & Video 360 is specifically designed to diagnose issues with Programmatic Guaranteed deals, including under-delivery. It provides insights into potential problems like bid rejections, targeting conflicts, and pacing issues, offering a centralized tool for investigation. While checking for multiple targeting assignments on the line item might be a contributing factor, the Deal Troubleshooter would highlight this and other potential issues more comprehensively. Reviewing campaign-level targeting is too broad; the problem is likely specific to the deal and its line item. Contacting the publisher is a later step, after you've exhausted your internal diagnostic tools.