在请求官方【https://api.mch.weixin.qq.com/v3/combine-transactions/jsapi】合单下单-JS支付API，一直报400 Bad Request错误

我的header为：【metaJson为官方php提供SDK，传过去为了签名，所以这个应该没错，我用官方phpSDK进件和进件查询请求接口都正常了，到这个合单就包400错误，按跟进件的POST请求一样啊】

"Accept": "application/json",
"Content-Type": "application/json",
"Wechatpay-Serial": "5CFB23F5EFE777A2651C4FE409D9FD6A007FC0C3",
"metaJson": "{\"combine_appid\":\"wx09f6dc683d4ab4d8\",\"combine_mchid\":\"1557374351\",\"combine_out_trade_no\":\"flq_1584957318\",
\"scene_info\":{\"device_id\":\"XCX:1\",\"payer_client_ip\":\"121.207.122.155\"},\"sub_orders\":[{\"mchid\":\"1557374351\",\"attach\":
\"599\",\"amount\":{\"total_amount\":10,\"currency\":\"CNY\"},\"out_trade_no\":\"fl12q_1584957318\",\"sub_mchid\":\"1581147271\",
\"detail\":\"\",\"profit_sharing\":true,\"description\":\"\\u6811\\u8102\\u7ebd\\u626324L\"}],\"combine_payer_info\":
{\"openid\":\"oRL0J41MdqQ1TfwoFf0goL2k1IPg\"},\"time_start\":\"2020-03-23T17:59:60+08:00\",\"time_expire\":
\"2020-03-24T17:59:60+08:00\",\"notify_url\":\"https:\\/\\/api.fuliaoquan.com\\/\",\"limit_pay\":[\"no_debit\"]}"

json为

{
    "combine_appid": "wx09f6dXXXXd4ab4d8",
    "combine_mchid": "15573***51",
    "combine_out_trade_no": "f_1584956927",
    "scene_info": {
        "device_id": "XCX:1",
        "payer_client_ip": "125.206.122.155"
    },
    "sub_orders": [
        {
            "mchid": "15573**351",
            "attach": "599",
            "amount": {
                "total_amount": 10,
                "currency": "CNY"
            },
            "out_trade_no": "f2_1584956927",
            "sub_mchid": "1581**7271",
            "detail": "",
            "profit_sharing": true,
            "description": "树脂纽扣24L"
        }
    ],
    "combine_payer_info": {
        "openid": "oRL0J41MdqQ1TfwoFf0goL2k1IPg"
    },
    "time_start": "2020-03-23T17:59:60+08:00",
    "time_expire": "2020-03-24T17:59:60+08:00",
    "notify_url": "https://api.XXX.com/",
    "limit_pay": [
        "no_debit"
    ]
}

按官方的JSON实例，没有必填的参数也填上去了，回调地址写的是一个官网，还没错回调，按理说现在回调地址不会请求校验把。

实在想不出哪里出问题了！还是参数错了。因为商户进件接口都是这样请求，都正常返回的！