Error in '<script src="{process.env.BROWSER_REFRESH_URL}"></script>'

[tik9]

I get in the console:
localhost/:18 GET http://localhost:5000/%7Bprocess.env.BROWSER_REFRESH_URL%7D 404 (Not Found)
It seems that the curly braces are interpreted the wrong way. Page is not refreshed, but in Terminal I get:
[browser-refresh] Server is ready. Page refresh triggered over WebSockets connection.
[browser-refresh] Triggering refresh of client pages...
[browser-refresh] Refresh triggered

What can I do?