In the app: Admin panel → Integraciones → «Servidor de juego (FiveM)». Only the server owner or an admin with «Gestionar el servidor».
Pick the scopes and, if you want, a label (up to 80 characters) and the IPs it works from (up to 20 IPs or CIDR ranges, IPv4 or IPv6; empty = from anywhere).
The key (gm_ followed by 4 characters, an underscore and 48 more) is shown ONCE. Blixye only stores its fingerprint: if you lose it, revoke it and create another.
When you create it, the app gives you the server.cfg block already written (set blixye_game_token "…" and ensure blixye_telefono) to paste as is (The server.cfg).
A server can have up to 10 active keys. Revoking one takes effect immediately.