I tried today for the first time to "connect" a backend (Flask) with a frontend (React). I have a Flask server running on my localhost.

Folder structure looks like this:

So now I have coded a mini Flask server

Afterwards I wanted to access the built-in JSON in the frontend with "fetch

To let React know where the backend is located, I specified the connection in package.json ("proxy": "http://localhost:5000/",)

according to the tutorial from which i got this code, it should work now. Unfortunately I get the error written above.

i tried many things i found in the internet like controling the JSON formatting and so on but everythign seems fine. i also had a problem that when i put after localhost:500/members and in the fetch also "/members" instead of "/" i got a server 500 error back. i could resolve or rather bypass by just simply put "/" in my fetch and backend code.