The 
Ad Exchange Seller REST API is deprecated. Existing API clients should migrate to the 
DoubleClick for Publishers API before July 26, 2018. After this date, all requests to the Ad Exchange Seller REST API will return errors.
This 
migration guide provides instructions for getting started, as well as a mapping of each Ad Exchange reporting metric to its equivalent in the DFP API. 
For more details about reporting in the DFP API, see the 
reporting guide.
For general assistance with the DFP API or your migration, reach out on our 
developer forum.