OpenRefine - invalid JSON?

Question

Please help me to detect what is wrong with this JSON that I want to apply in OpenRefine. I get message that this JSON is invalid and cannot apply it, but it is not obvious to me what is wrong with format of JSON? This is how the JSON looks like. In reality, it is much bigger, but it is formatted like this:

{
  "entries": [
    {
      "op": "core/column-remodeling",
      "description": "Text transform on cells in column First Name using expression grel:value.trim().toTitleCase()",
      "engineConfig": {
        "facets": [],
        "mode": "row-based"
      },
      "columnName": "First Name",
      "expression": "value.trim().toTitleCase()",
      "onError": "set-to-blank",
      "repeat": false,
      "repeatCount": 10
    },
    {
      "op": "core/column-remodeling",
      "description": "Text transform on cells in column First Name -MyData using expression grel:value.trim().toTitleCase()",
      "engineConfig": {
        "facets": [],
        "mode": "row-based"
      },
      "columnName": "First Name -MyData",
      "expression": "value.trim().toTitleCase()",
      "onError": "set-to-blank",
      "repeat": false,
      "repeatCount": 10
    },
    {
      "op": "core/column-addition-by-fetching-urls",
      "description": "Create column First Name based on column ['First Name', 'First Name -MyData'] using expression grel:\"unique(coalesce(cells['First Name'].value.trim().toTitleCase(), '').toString() + ' | ' + coalesce(cells['First Name -MyData'].value.trim().toTitleCase(), '').toString().split(' | '))\"",
      "engineConfig": {
        "facets": [],
        "mode": "row-based"
      },
      "newColumnName": "First Name",
      "columnInsertIndex": -1,
      "baseColumnName": "First Name",
      "urlExpression": "unique(coalesce(value.trim().toTitleCase(), '').toString() + ' | ' + coalesce(cells['First Name -MyData'].value.trim().toTitleCase(), '').toString().split(' | '))",
      "onError": "set-to-blank",
      "delay": 0,
      "cacheResponses": false,
      "httpHeadersJson": "{}"
    },
    {
      "op": "core/column-remodeling",
      "description": "Text transform on cells in column Last Name using expression grel:value.trim().toTitleCase()",
      "engineConfig": {
        "facets": [],
        "mode": "row-based"
      },
      "columnName": "Last Name",
      "expression": "value.trim().toTitleCase()",
      "onError": "set-to-blank",
      "repeat": false,
      "repeatCount": 10
    },
    {
      "op": "core/column-remodeling",
      "description": "Text transform on cells in column Last Name -MyData using expression grel:value.trim().toTitleCase()",
      "engineConfig": {
        "facets": [],
        "mode": "row-based"
      },
      "columnName": "Last Name -MyData",
      "expression": "value.trim().toTitleCase()",
      "onError": "set-to-blank",
      "repeat": false,
      "repeatCount": 10
    },
    {
      "op": "core/column-addition-by-fetching-urls",
      "description": "Create column Last Name based on column ['Last Name', 'Last Name -MyData'] using expression grel:\"unique(coalesce(cells['Last Name'].value.trim().toTitleCase(), '').toString() + ' | ' + coalesce(cells['Last Name -MyData'].value.trim().toTitleCase(), '').toString().split(' | '))\"",
      "engineConfig": {
        "facets": [],
        "mode": "row-based"
      },
      "newColumnName": "Last Name",
      "columnInsertIndex": -1,
      "baseColumnName": "Last Name",
      "urlExpression": "unique(coalesce(value.trim().toTitleCase(), '').toString() + ' | ' + coalesce(cells['Last Name -MyData'].value.trim().toTitleCase(), '').toString().split(' | '))",
      "onError": "set-to-blank",
      "delay": 0,
      "cacheResponses": false,
      "httpHeadersJson": "{}"
    }
  ]
}