Ошибка при создании произвольного поля через API

POST http://hst-api.wialon.com/wialon/ajax.html HTTP/1.1
Host: hst-api.wialon.com
Proxy-Authorization: NTLM <удалено>
User-Agent: 1C+Enterprise/8.3
Accept: */*
Connection: Keep-Alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 180

sid=<удалено>&svc=item/update_custom_field&params={
"itemId": "12074596",
"id": "1",
"callMode": "create",
"n": "ID объекта",
"v": "12074596"
}

HTTP/1.1 200 OK
Date: Mon, 23 Jul 2018 08:07:44 GMT
Content-Type: application/json
Content-Length: 12
Connection: keep-alive
Cache-Control: no-cache
Server: adf_http_server/4.3.0205

{"error":6}