In order to simplify integration with GAM account via Google API we've prepared this separate page.
GAM Link is the entity that holds information about your GAM Account (s) - called "Link". You may create several Links is you use more than one GAM account for your business or represent several third-party publishers that use their own GAM accounts.
Once created, a Link might be used multiple times for "Site" creation and update. No need to add all the API link assets each time anymore.
After you click "Submit" a new Link is available for your convenience. You may use it while creating your GAM API Site.