wrong url and 404 err

Hi! How your aplication always get right url? My problem is that without

 axios.defaults.baseURL = “http://localhost:5000”;
i can`t get data from backend because without it my app always try to get data from localhost:5173(my frontend url).
Also on my web site on vercel(dont use heroku because of recent leak of data) I can`t get data from backend. i just get 404 error