posting multi JSON and work with web-api

how should I post Json for multi record

I have one Product_ID and one Group_ID, and features of attribute, how should I post or create Json for posting

my Json code:

{
    'objFeturesItemsPostwithStyle': [{
        'catname': 'Category_name',
        'catId': 'n',
        'attrName': 'some attr name',
        'attrId': '0',
        'valueId': '0',
        'valueName': 'ggg',
        'unitId': '',
        'unitName': ''
    }
,
{
        'catname': 'Category_name',
        'catId': 'n',
        'attrName': 'some attr name',
        'attrId': '0',
        'valueId': '0',
        'valueName': 'ggg',
        'unitId': '',
        'unitName': ''
    }
],
    'Product_ID': '14618',
    'Group_ID': '45',

}

what's wrong?