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.text)

{
  "id": "<string>",
  "display_type": "<string>",
  "pipeline_id": "<string>",
  "schema": {
    "additionalProperties": {},
    "category": "<string>",
    "categoryPriority": 123,
    "default": "<string>",
    "definitions": {},
    "description": "<string>",
    "enum": [
      {}
    ],
    "hints": [
      "<string>"
    ],
    "maxProperties": 123,
    "minProperties": 123,
    "oneOf": [
      {
        "type": "string",
        "title": "<string>",
        "description": "<string>",
        "default": "<string>",
        "category": "<string>",
        "categoryPriority": 123,
        "hints": [
          "<string>"
        ],
        "unsafe": true,
        "oneOf": [
          {
            "type": "string",
            "title": "<string>",
            "description": "<string>",
            "default": {},
            "category": "<string>",
            "categoryPriority": 123,
            "hints": [
              "<string>"
            ],
            "unsafe": true
          }
        ]
      }
    ],
    "properties": {},
    "propertyGroups": [
      {
        "label": "<string>",
        "properties": [
          "<string>"
        ]
      }
    ],
    "required": [
      "<string>"
    ],
    "title": "<string>",
    "type": "array",
    "unsafe": true
  }
}