unable to make an index creation about lua-mongo HOT 2 CLOSED

client:command [[
{
    createIndexes: <collection>,
    indexes: [
        {
            key: {
                <key-value_pair>,
                <key-value_pair>,
                ...
            },
            name: <index_name>,
            <option1>,
            <option2>,
            ...
        },
        { ... },
        { ... }
    ],
}
]]

nbclient=OP_FindClient("ClientName")
client=op_client[nbclient]  -- get the client among multiple ones
query = [[
	{
	    "createIndexes":"sites",
		"indexes" : [
			{
			"key" : {
				"name":1,
				"addr":1,
				"ville":1
				},
				"name":"idx"
			}
			]
	}
	]]
queryBSON = mongo.BSON(query)
ret = client:command("myDBname",queryBSON)