Returned empty attributes array

Hi every one! I have some problem.
I was develop some app for customer who use this API.
After request to API i get response, at first at looks good, but, array field “attrinutes” was returned empty.
I was testing in Postman, response looks good, with the attributes and all include.
App in C#, use RestSharp.
What can it be ? Maybe some one have same problem here?