Create a custom field relationship to list(s)

{
    "fieldRel": {
        "field": 8,
        "relid": 2
    }
}

{
    "fieldRel": {
        "relid": 2,
        "field": 8,
        "cdate": "2019-02-01T08:39:25-06:00",
        "links": [],
        "id": "19"
    }
}