{\"mchid\"\n"

从日志提示上看，你初始化Builder::factory([])商户号 可能没取到，另外建议装个dev包，IDE就带提示了

https://github.com/TheNorthMemory/wechatpay-openapi/blob/master/src/V3/Pay/Transactions/Jsapi.php#L17-L58

    public function post(array $options = [
        'json' => [
            'appid' => 'wxd678efh567hg6787',
            'mchid' => '1230000109',
            'description' => 'Image形象店-深圳腾大-QQ公仔',
            'attach' => '自定义数据',
            'out_trade_no' => '1217752501201407033233368018',
            'amount' => [
                'total' => 100,
                'currency' => 'CNY',
            ],
            'time_expire' => '2018-06-08T10:34:56+08:00',
            'notify_url' => 'https://www.weixin.qq.com/wxpay/pay.php',
            'goods_tag' => 'WXG',
            'limit_pay' => ['string'],
            'support_fapiao' => true,
            'detail' => [
                'cost_price' => 608800,
                'invoice_id' => '微信123',
                'goods_detail' => [[
                    'merchant_goods_id' => '商品编码',
                    'wechatpay_goods_id' => '1001',
                    'goods_name' => 'iPhoneX 256G',
                    'quantity' => 1,
                    'unit_price' => 828800,
                ],],
            ],
            'scene_info' => [
                'payer_client_ip' => '14.23.150.211',
                'device_id' => '013467007045764',
                'store_info' => [
                    'id' => '0001',
                    'name' => '腾讯大厦分店',
                    'area_code' => '440305',
                    'address' => '广东省深圳市南山区科技中一道10000号',
                ],
            ],
            'payer' => [
                'openid' => 'oUpF8uMuAJO_M2pxb1Q9zNjWeS6o',
            ],
        ],
    ]): ResponseInterface;