List Contact's custom fields

Example response

{
  "_links": {
    "self": "https://yourCompany.api.frontapp.com/custom_fields"
  },
  "_results": [
    {
      "_links": {
        "self": "https://yourCompany.api.frontapp.com/custom_fields/fld_co0e"
      },
      "id": "fld_co0e",
      "name": "Customer plan",
      "description": "The billing plan of the customer",
      "type": "enum",
      "values": [
        {
          "value": "Enterprise",
          "label": "Customer plan"
        }
      ]
    }
  ]
}