Installing the Google Tag manager server container does not require any Client Id. Users have to create a container within the GTM interface and then automatically provision the server. To make the process easier at Gaasly we use stape.io hosting services. Client Id also refers to Google Analytics user identification. With server-side tracking, Client Id is still a valid concept but works differently: rather than being configured on the web browser, now Client Id cookie is configured on the server, which is a first-party context.