import requests

url = "https://{FUSION HOST}/api/custom-rule-types"

payload = {
    "id": "custom-rule-type",
    "pipeline_id": "custom-rule-pipeline",
    "display_type": "My Custom Rule",
    "schema": {
        "type": "object",
        "properties": {
            "custom_param1": {
                "type": "string",
                "title": "Manufacturer",
                "description": "The manufacturer of the product this rule action applies to."
            },
            "custom_param2": {
                "type": "string",
                "title": "Type",
                "description": "The type of product this rule action applies to."
            }
        }
    }
}
headers = {
    "Authorization": "Basic <encoded-value>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())

{
  "id": "<string>",
  "display_type": "<string>",
  "pipeline_id": "<string>",
  "schema": {}
}