$params = [
    'mchid' => $wechat_config['mchid'],
    "out_trade_no" => $order['order_sn'],
    'appid' => $wechat_config['appid'],
    "description" => $order['desc'],
    "notify_url" => Env::get("notify.wechat"),
    'amount' => [
        'total' => intval(bcmul($order['amount'], 100)),
        'currency' => 'CNY',
    ],
];
$res = $wechat_client->v3->pay->transactions->app->post([
    'json' => $params,
]);
return [$res->getStatusCode(), $res->getBody(), $params];

这样结构应该是没有问题才对，但是没有prepay_id返回，是为什么？