I am trying to set the URL of the API at runtime. I followed this tutorial which solves the exact problem I have, but still, the variable is undefined.

I put the file with enviromental variable in script in index.html (EDITED)

<script src="%PUBLIC_URL%/env-config.js"></script>

Inside of which is (after the image starts through Docker) something like this:

window._env_ = {
    API_URL: "my-awesome-url" // filled by bash script defined in ENTRYPOINT
}

But when I want to use it in the React app I get something like cannot read property of undefined API_URL. When I try to access the window object in console, I can see, the _env_ variable is not present in the object. What am I missing?