Hello @Super Admin ,
Thanks for reaching out.
The ClassicAdministrators API only returns email address and PUID as of now.
Sample:
{"value":[{"properties":{"emailAddress":"abc@outlook.com","role":"ServiceAdministrator"},"id":"/subscriptions/9xxx7b-f0e7-4xx0-9038-abxxxd95e7c/providers/Microsoft.Authorization/classicAdministrators/00034001AC4EF0DD","type":"Microsoft.Authorization/classicAdministrators","name":"00034001AC4EF0DD"}]}
I would recommend you to please comment and/or up-vote the below user voice items to increase the priority of feature implementation.