Create standard request as it is in documentation, but use pie graph instead.

{
    "jsonrpc": "2.0",
    "method": "graph.create",
    "params": {
        "name": "graph",
        "width": 100,
        "height": 100,
        "graphtype": "2",
        "gitems": [
            {
                "itemid": "22828",
                "color": "00AA00"
            }
        ]
    },
    "auth": "038e1d7b1735c6a5436ee9eae095879e",
    "id": 1
}

And observe error:
Undefined index: type [... → CFrontendApiWrapper->create() → CApiWrapper->__call() → CFrontendApiWrapper->callMethod() → CApiWrapper->callMethod() → CFrontendApiWrapper->callClientMethod() → CLocalApiClient->callMethod() → call_user_func_array() → CGraphGeneral->create() → CGraph->validateCreate() → CGraphGeneral->validateCreate() → CGraphGeneral->checkAxisItems() in include\classes\api\services\CGraphGeneral.php:298]