Custom fields returns empty in Create Ticket API

Custom fields returns empty in Create Ticket API

Am sending custom fields like below in create ticket API but am getting empty response. Is there any error in my request?

Request:

 "category": "general",
    "cf": {
        "cf_storeid": "1001",
        "cf_storename": "Test"
    },
    "status": "Open"

Response:
    "cf": {},