Type of CTV Advertising ID. Platform-native values (e.g., 'tifa' for Samsung Tizen, 'rida' for Roku, 'afai' for Amazon Fire TV, 'vida' for Vizio, 'lgudid' for LG, 'atv' for Apple TV, 'msai' for Microsoft Xbox, 'dpid' for various) or publisher-generated. 'untyped_ctv_id' is the fallback when the platform is unknown.