As part of the effort to increase reporting transparency, buyers are required to declare any advertising agency associated with a creative. Declaration can occur either at upload time with Google-hosted creatives or within the BidResponse for third-party ads.
The worldwide agencies list maps each agency to a unique identifier.
Declaration in the creative submission API
Agency declaration can occur when a creative is submitted via the creative submission API.
Include this line in your POST:
"agencyId": {integer},
Declaration in the BidResponse
To declare the agency in the BidResponse, include the attribute:
optional int64 agency_id = 16;
If this ad has no associated agency, set a null value rather than leaving this field unspecified:
agency_id: 1
If the agency has already been specified in the creative, a non-null value in the `BidResponse` will override the declaration made at the creative level.