Failing to use fetch_size parameter with query

[ofir2471]

I'm trying to use the fetch_size parameter in my payload, but keep getting:

this is the query I'm trying to use:
curl -XPOST -u "username:password" -H "Content-Type: application/json" https://myurl.com/_opendistro/_sql -d "{ "query" : "SELECT id FROM db*", "fetch_size": 5}".
From your documentation: Cursor - fetch_size.
I'm working with opendistro on elasticsearch.