Credentials are stored only on this device (localStorage). Z-Library blocks direct browser calls, so requests go through a relay. Public relays are unreliable — for a relay that actually works, deploy your own free Cloudflare Worker (no app needed): create a Worker at dash.cloudflare.com, paste the proxy code (ask me for it), then put its URL here ending in ?url= (e.g. https://my-proxy.workers.dev/?url=). If a domain stops working, Z-Library rotated it — try z-lib.gs, 1lib.sk, z-library.sk. Downloads are limited per day by your account.