Dealing with Custom Fields in Deluge

Dealing with Custom Fields in Deluge

Greetings

I'm trying to add expenses from my creator app to zoho books, in zoho books i have some custom fields for the expenses that i'd like to set when creating the entry. but i'm unable to get it to work. 
and it says i must include my custom fields in an array which i did like that (using the API Field Name of my custom field)

  1. dataMap.put("custom_fields":[{"cf_employee_name":"Test Name"}]);
I also tried this
  1. data.put("custom_fields",[{"customfield_id": "cf_employee_name",
  2.             "value": "Test Name"}]);

both ways don't work and i end up getting an empty value for the custom field, i think the value of the customfield_id should be numeric but i don't know where to get this exactly..

How can i achieve what i want?