I deployed my website on vercel, and sadly this happens to me and can't know the reason

so i made an api endpoint /auth/{provider} e.g. /auth/discord and it redirects you to the uri page for that provider to authenticate yourself.
and to make it easier for the user i made it using a new popup window using normal js code
window.open("/auth/discord") and suddenly the page that opens it completly empty page with a response but surely not coming from vercel or idk how to describe it but when i go manually to /auth/discord and open the popup it works fine, so what's the issue here and how to fix it?