从json数组获得结果

Someone, please help me to get only the order id from this array:

array(2) { 
    ["success"] => int(1) 
    ["return"] => array(1) { 
        [100010973975966] => array(7) { 
            ["pair"] => string(8) "doge_btc"
            ["type"]=> string(3) "buy"
            ["start_amount"]=> int(300)
            ["amount"]=> int(300)
            ["rate"]=> float(3.9E-7)
            ["timestamp_created"]=> string(10) "1530443432"
            ["status"]=> int(0) 
        } 
    } 
} 

I need to extract only 100010973975966 as a variable. I am using this code to get this data from yobit:

$order_info = $yobit->privatePostOrderInfo(
    array(
        "nonce" => time(),
        "order_id" => $result["return"]["order_id"]
    )
);

Thanks a lot!

You mean 100010973975966? You could get that with array_keys( $result["return"] )[0].

Looking at the image in the comments, $order_info is the variable that contains the array with the data.

To get the order id which is the key from the array $order_info['return'] you might use key:

$order_info = [
    "success" => 1,
    "return" => [
        "100010973975966" => [
            "pair" => "doge_btc"
            // etc..
        ]
    ]
];

$order_id = key($order_info['return']);
echo $order_id; // 100010973975966

Demo