Netsuite: Add new value in custom list via REST webservice

Question

I am new to netsuite. I am using Netsuite REST webservice to post my application data to netsuite. So far I have managed to create customer, add address and get reference to different custom fields internal Ids.

One of the things I want to achieve is to look for a value in "Custom List" and if the value doesn't exist, then create a new value under that Custom List.

I have managed to identify whether the value exist in custom list or not using following endpoint

GET /record/v1/<custom_list_id>?q=name IS "<value>" 

But when I try to call POST on the same endpoint with body {"name": "<New value>" } I get following error

{
    "type": "https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.5.1",
    "title": "Pre-processor error occured! Unknown custom record type Error ID: xxxxxxxxxxxx",
    "status": 500,
    "o:errorCode": "UNEXPECTED_ERROR"
}

I have found some examples of how to create a new Custom Record Type, but none about Custom List.