为什么我写的这个接口访问方法在有一些用户那里会出现res.statusCode = 400的情况了？

function request(url, postData, message, doSuccess, doFail, doComplete) {

var baseUrl = getBaseUrl();

var xml = sign.xmlStr(postData, url);

wx.request({

url: baseUrl + '?op=' + url,

data: xml,

method: 'POST'

header: {

'content-type': 'application/soap+xml; charset=utf-8'

},

dataType: 'xml'

success: function (res) {

if (typeof doSuccess == "function") {

if (message != "") {

wx.hideLoading();

}

if (res.statusCode == 200) {

} else {

wx.showToast({

icon: 'none'

title: url + res,

})

doFail();

}

}

},

});