If there’s under delivery, you'll be paid for the impressions delivered, and adjustments may be required to meet the expected impressions such as a make good (s) or AV (added value) in the form of social media posts or additional episodes at no cost to the advertiser. Over delivery is appreciated, though payment will be based on the original offer. Success is measured using tools like Podscribe and Spotify Ad Analytics, considering factors like impression delivery, campaign timeliness, web traffic conversion, and advertiser ROI.