How to search using custom fields in Zoho Desk (via Deluge scripting)?

How to search using custom fields in Zoho Desk (via Deluge scripting)?

In Zoho Desk, I have an account-level custom numeric field, called 'cf_vl_client_id', which is used to store the internal Client ID generated by our system. When I am trying to search records (in the Accounts module) using this custom field, I am constantly getting an error:
  1. zoho.desk.searchRecords(deskOrgId, "accounts", {"cf_vl_client_id": 1000});
Error:
  1. {"errorCode":"UNPROCESSABLE_ENTITY","message":"The value passed for the 'cf_vl_client_id' parameter is invalid."}
Surprisingly, I am able to find records using accountName:
  1. zoho.desk.searchRecords(deskOrgId, "accounts", {"accountName": "saurabh"});
Therefore, I am pretty sure that my syntax for searching via custom-field is incorrect. Unfortunately, the docs do not seem to cover this scenario.

Any help, please?