Custom parameters are a type of URL parameter that add dynamic data to your landing page URLs or tracking URLs. They're similar to ValueTrack parameters, except you choose the values your custom parameters record when someone clicks on your ad.
Only engines with shared templates provide custom parameters, and Search Ads 360 only displays and manages custom parameters for some of its supported engines. Learn more
In engine accounts with shared templates, Search Ads 360 uses custom parameters to store unique IDs for each keyword and other items it manages. The custom parameter is included in the Search Ads 360 clickserver URL, so when a search matches a keyword and a visitor clicks an ad, Search Ads 360 uses the unique IDs in the custom parameters to attribute the click to the keyword.