Invalid syntax in working construction. SQL Server 16

I keep getting 'incorrect syntax near "$[0]".'

Here is the code.

INSERT INTO CompuconTaxi.dbo.Regions (name, region_name, polygon)
SELECT
    'tes' AS name,
    'asd' AS region_name,
    geography::STPolyFromText('POLYGON ((' + STRING_AGG(CAST(Long + ' ' + Lat as varchar(max)), ',') + '))',4326).ReorientObject() AS polygon 
FROM
(
    SELECT 
        Long,
        Lat
    FROM
       OPENJSON(N'{
    "type": "Feature", "properties": {"region_name": "test2", "name": "test" }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 23.8580303, 38.1225949 ], [ 23.8578422, 38.1225496 ]]] }
}', '$.geometry.coordinates[0]')
    WITH
            (
                Long varchar(100) '$[0]',
                Lat varchar(100) '$[1]'
            )
)d

Here is tutorial link i user, to produce this code

The trouble is that this code works as intended, which is bullshit. Any ideas?

SELECT 
        Long,
        Lat
    FROM
       OPENJSON(N'{
    "type": "Feature", "properties": {"region_name": "test2", "name": "test" }, "geometry": { "type": "Polygon", "coordinates": [ [ [ 23.8580303, 38.1225949 ], [ 23.8578422, 38.1225496 ]]] }
}', '$.geometry.coordinates[0]')
    WITH
            (
                Long varchar(100) '$[0]',
                Lat varchar(100) '$[1]'
            )