Change default env var PUBLIC_URL

I want to change the PUBLIC_URL env var name to use CDN_URL but when run the refine dev script I have this error

Failed to decode param '/%CDN_URL%/env-config.js'

Failed to decode param '/%CDN_URL%/env-config.js'

Failed to decode param '/%CDN_URL%/env-config.js'

Failed to decode param '/%CDN_URL%/env-config.js'

The env-config file has this info

window.env = {
    API_URL:'https://....',
};

window.env = {
    API_URL:'https://....',
};

window.env = {
    API_URL:'https://....',
};

window.env = {
    API_URL:'https://....',
};

And is localated in the public folder.