Python Flask Cors error – set according to documentation

I have created API using Flask in Python. Now I am trying to create front end, where I want to call API. I set CORS according Flask-Cors documentation, unfortunately it doesn’t work.

from flask_cors import CORS
CORS(app)

I got this error
CORS error – Safari

CORS error – Chrome

I have found some similar topics, where was some solution. I have tried, but neither of them work for me. E.g.

CORS(app, origins=['http://localhost:4200'])
app.config['CORS_HEADERS'] = 'Content-Type'

I have also tried cross_origin decorator, but it doesn’t work as well.

@app.route("/login", methods = ["POST"])
@cross_origin(origin='*')
def login():
    credentials = request.get_json()
    ....

Could someone help me, how to solve this problem?