Как исправить Access to fetch from origin has been blocked by CORS?

Question

[Ася]

Я запускаю фласк на

localhost:5000

и npm run start на

localhost:3000

у меня выпадает ошибка:

Access to fetch at 'localhost:5000/api/app' from origin 'localhost:3000' has been blocked by CORS policy: The 'Access-Control-Allow-Origin' header contains multiple values 'localhost:3000, localhost:3000', but only one is allowed. Have the server send the header with a valid value, or, if an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

хедеры добавляю такие

response.headers.add('Access-Control-Allow-Origin', 'https://localhost:3000')
    response.headers.add('Access-Control-Allow-Credentials', 'true')
    response.headers.add('Access-Control-Allow-Headers', 'Content-Type,Authorization')
    response.headers.add('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE,OPTIONS')

Как исправить?

Comments

[planc]

The 'Access-Control-Allow-Origin' header contains multiple values 'localhost:3000, localhost:3000', but only one is allowed.

хедер Access-Control-Allow-Origin отдает несколько значений 'localhost:3000, localhost:3000', а должен отдавать только одно

[Ася]

planc, я это вижу, но не понимаю как исправить ?