JSON in API to Change Platform Endpoint

I'm using the configuration store API to change the platform endpoint and having trouble getting the JSON formatting right. This is the JSON example from the docs.
{
"value" : "string"
}

When I use the API to list the config store it looks like this.
{
"values": [{
"changed": false,
"name": "https_port",
"value": "9243"
}, {
"changed": true,
"name": "cname",
"value": "prod2"
}]
}

I've tried a combination of values[1].value with no success.

Assuming you're trying to change the parameter cname, does the following work?

curl -XPOST -k -u admin:PASS 'https://HOST:12443/api/v1/platform/configuration/store/cname' -d '{ "value": "NEW_VAL" }'

(docs)

If not how does it fail?

Yeah I wanted to change cname. After messing with it a bit more I got it to work. Thanks.