Issue with adding ISRC codes to MP4

Hi there. I downloaded Kid3 and opened my MP4 video file. When I click on "Add" (Add Frame) on the right side I do not see ISRC as an option. Whenever I see someone in an instructional video add ISRCs to their video, they have ISRC in their menu, however I do not. Any idea what could be going wrong here?

Thanks very much.