我怎么才能得到角9的圆球呢

我收到以下错误:

Access to XMLHttpRequest at 'http://localhost:40000/api/summaryCount/failed-requests' from origin
'http://localhost:3000' has been blocked by CORS policy: 
Response to preflight request doesn't pass access control check: 
No 'Access-Control-Allow-Origin' header is present on the requested resource.

我创建了一个proxy.conf.json文件,其中包含以下内容:

{"/api/*": {
    "target": "http://localhost:40000",
    "secure": false
  }
}

"proxyConfig": "proxy.conf.json"

在“发球”上:{“选项”{。。。。。。

最后,我修改了package.json,使“start”选项变成:

"start": "ng serve --proxy-config proxy.conf.json",

在创建HttpHeaders对象时,如果添加以下内容:

httpHeaders = new HttpHeaders().append('Access-Control-Allow-Origin', 'http://localhost:3000').....

这仍然没有区别。

有人能告诉我我错过了什么吗。