Flutter：请求的资源上不存在“Access-Control-Allow-Origin”标头

我已经使用 python Flask 创建了 REST GET API，它的代码如下

app = Flask(__name__)
 
@app.route("/youtube")
def firstGetAPI():
 
    try:
        url = request.args.get('url')
        print(f'URL is {url}')
        res = "Success"
        response = flask.Response(res)
        response.headers.set('Access-Control-Allow-Origin', '*')
        response.headers.set('Access-Control-Allow-Headers', 'Content-Type,Authorization')
        response.headers.set('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE,OPTIONS')
        return response, 200
    except Exception as e:
        response = {"status":"Fail", "message":str(e)}
        return json.dumps(response)
 
if __name__ == "__main__":
    app.run(host='0.0.0.0', debug=True, port=8080)

现在在前端，Flutter 代码如下

child: ElevatedButton(
                child: const Text('Download'),
                onPressed: () async {
                  var header = {
                    'Access-Control-Allow-Origin': '*',
                    "Accept": "application/json"
                  };

                  var url = Uri.parse(
                      'http://192.168.2.237:8080/youtube?url=www.google.com');

                  print('URL is : ${url}');
                  var response = await http.get(url, headers: header);
                  print('Response status: ${response.statusCode}');
                  print('Response body: ${response.body}');
                },
              ),

我已经在 Chrome 浏览器上运行了这个，但我总是收到如下错误

     URL is : http://192.168.2.237:8080/youtube?url=www.google.com
:49831/#/:1 Access to XMLHttpRequest at 'http://192.168.2.237:8080/youtube?url=www.google.com'
 from origin 'http://localhost:49831' 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.
browser_client.dart:74 GET http://192.168.2.237:8080/youtube?url=www.google.com net::ERR_FAILED

抱歉，我不知道这是 Python 还是 Flutter 的问题，我在这里合并了这两个代码，谢谢