Querying JSON array values in a mock API not working

Hi,
My requirement is to have a json array in the dataset. But when I try to write formula on API schema to get the values inside json array using a primary key (like customer_id), I am getting null always

from_dataset("A 1000 Credit cards","creditinfo.name",cardID:request_params['cardid'])

In the above formula creditinfo is a json array and name is one the field inside json array. cardID is what I am using in my API.