To make sure mobile-optimized creatives are appearing on mobile websites and delivering properly, you should examine your trafficking settings in Campaign Manager 360 to determine if mobile-friendly sizes and formats are included.

• Configure your account within Campaign Manager 360 to include apps, mobile devices, and tablets.
• Review your Cross-environment Report to check on campaign effectiveness across all environments, including mobile.
• Use mobile-friendly sizes and formats when organizing your campaign in Campaign Manager 360.
• Examine your trafficking settings in Campaign Manager 360 to determine if mobile-friendly sizes and formats are included.

The correct answer is: Examine your trafficking settings in Campaign Manager 360 to determine if mobile-friendly sizes and formats are included

Explanation: The answer “Examine your trafficking settings in Campaign Manager 360 to determine if mobile-friendly sizes and formats are included” is partially correct but not the absolute first consideration.

The very first thing to check is the targeting settings of your existing ads and placements. You need to ensure that mobile environments (like mobile web and mobile apps) are included in the targeting criteria for the placements where these mobile-optimized creatives are assigned. If mobile isn’t targeted, the ads won’t serve on mobile devices, no matter how mobile-friendly their sizes and formats are.

While confirming mobile-friendly sizes and formats is important for new creatives, for existing ones that could already be serving, verifying the targeting is the immediate first step to ensure they are even eligible to appear on mobile inventory.