Final answer:
To add third-party verification to a creative in Campaign Manager, you would embed the verification code directly into the creative during the upload process, rather than through the Campaign Manager API, DV360 settings, or other means.
Step-by-step explanation:
To add third-party verification to a creative when Campaign Manager is your ad server, you would do so by directly embedding verification code into the creative. While APIs are useful for many tasks in Campaign Manager, they are not the method used to integrate third-party verification. DV360 settings are related to a different product called Display & Video 360, which works in tandem with Campaign Manager but does not control creative settings directly within it. Instead, third-party verification is often integrated during the creative upload process, where you would direct the ad server to call the third-party verification service.