Reporting functionality via the APIs is currently limited to Ad Exchange Buyer II API's
RTB Troubleshooting resources. These can be used to retrieve information similar to what you might see in the UI's
RTB Breakout feature. When you say "day wise cost metrics", I assume you're referring to your daily spend on Real-time Bidding? At this time, there is no programmatic means of retrieving that information. The
reporting feature in the UI does allow you to view cost transparency metrics that could be closer to what you're looking for, but is not a topic we would cover here. If you need more assistance on learning to use that feature of the UI, I would recommend either contacting your Technical Account Manager or filling out
this support form if you don't have one.