Update Eloqua action service configuration with custom object record definition return error

We are developing Eloqua App with an action service. When I create action service from campaign canvas, makes changes through the Configure URL that require custom object field, and then trigger updating action service configuration with custom object record definition, it returns error. This is my request:

POST https://secure.p01.eloqua.com/api/cloud/1.0/actions/instances/${INSTANCE_ID}{    "recordDefinition": {         "Email": "{{CustomObject[5].Field[75]}}"    },   "requiresConfiguration": false}

But I get ML Statements must have a Contact root error:

{    "failures": [        {            "field": "Email",            "stackTrace": [                {                    "field": "recordDefinition"                }            ],            "value": "{{CustomObject[5].Field[75]}}",            "constraint": "ML Statements must have a Contact root."        }    ]}

I have been survey related problem in the community and document