在PodioAppField :: update上找不到路径

I am following the documentation https://developers.podio.com/doc/applications and the given models from the SDK.

Im trying to add a new app to an existing app reference like so:

$attributes = array( 
            "referenced_apps" => array(ref_app_id1 , ref_app_id2)                        
        );

PodioAppField::update( 123 ,  'my_external_id' ,array (
                                                    "settings" => $attributes
                                               ));

But will receive the following error

Uncaught PodioNotFoundError: "No matching operation could be found. The path '/app/123/field/my_external_id' was not found.."

My app_id and external_id are correct.

TIA

It requires field_id instead of external_id.