Flask CORS策略阻止请求问题求助

各位大佬好，我现在卡到一个非常头疼的问题上了：我想通过CORS配置让我的Flask-Rest API接收来自网站的请求，但一直被CORS策略拦截，完全没法正常通信，求各位帮忙看看！

我的网站部署在https://example.com，而REST API是跑在https://example.com:5000的。

下面是我写的Python代码（用了Flask RestAPI）：

app = Flask(__name__)

app.config.from_object(ProductionConfig)

CORS(app,resources={r"/*": {"origins": "*"}},supports_credentials=True)

api = Api(app)

@app.after_request
def add_cors_headers(response):
    response.headers.add('Access-Control-Allow-Origin',"https://example.com")
    response.headers.add('Access-Control-Allow-Credentials','true')
    response.headers.add('Access-Control-Allow-Methods',"GET,POST,OPTIONS,HEAD")
    response.headers.add('Access-Control-Allow-Headers',"Origin, X-Requested-With, Content-Type, Accept, Authorization")

结果浏览器控制台一直报这个错误：

Access to fetch at 'https://example.com:5000/folders?page=1&limit=25&loader=false' from origin 'https://example.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

我实在搞不明白——明明我既通过CORS()初始化配置了跨域，又在after_request里手动加了Access-Control-Allow-Origin头，为什么控制台还会说“请求的资源上不存在'Access-Control-Allow-Origin'头”啊？

我现在急着把这个网站正式上线，真的需要大家的帮助，任何建议我都会非常感激！

备注：内容来源于stack exchange，提问作者Elcid_91