how to populate DropDown from API Call return JSON

Hi,

First I have created a Data Schema-Data Type named as Subjects with the fields as sbCode(String) and sbName(String)

Then I created App State of List<Subjects>, and created an API-Call which returning a json string as

"[{\"sbCode\":\"4\",\"subject_name\":\"Data Structure and Algorithms\"}]"

Then I created the DropDown Widget and in the option, I connected App State List<Subjects> with the field of sbName and on Page_load action calling API Json where I m trying to updateState of List<Subjects> but not getting any luck to populate the dropdown list of subjects.

Please guide me where I am doing wrong;