You created a line item in a Display & Video 360 mobile web campaign that accidentally targets mobile in-app. You remove that mobile in-app targeting at the insertion order level, yet the campaign in continuing to target mobile-in app. What's the issue here?

The correct answer is "It's impossible to modify existing line item targeting at the insertion order level" because targeting in Display & Video 360 is inherited downwards. While an insertion order can constrain the targeting of its child line items (e.g., an IO targets only males, so all its line items will also target only males), it cannot override or remove targeting that has already been set at the line item level. If a line item is explicitly set to target mobile in-app, removing mobile in-app targeting at the insertion order level will not remove it from that specific line item. The line item's specific targeting will take precedence within the broader constraints of the insertion order. "It's impossible to modify insertion order targeting at the line item level" is incorrect because line items do inherit and can further refine (but not contradict) insertion order targeting. "It's impossible to modify targeting once the campaign has line items assigned" is incorrect; targeting can be modified at various levels even after creation. "It's impossible to modify targeting for mobile in-app inventory at the line item level" is incorrect; mobile in-app targeting is a standard option available at the line item level.