Can i create custom ruleset via API in Free plan?

Developers API
1 
I'm creating custom ruleset via API in free plan it's give me a error message like : "not entitled to use the firewall custom phase"
URL : https://api.cloudflare.com/client/v4/accounts/<Account_ID>/rulesets
response is:
{
    "result": null,
    "success": false,
    "errors": [
        {
            "message": "not entitled to use the firewall custom phase"
        }
    ],
    "messages": null
}

can anybody help to resolve this error?