In Manage → Integrations → ER:LC. Only the owner can change it: save, change and test the key. Once saved it is never shown in full again, only its last 4 characters so you can recognise it; if you need it, get it again from ER:LC.
It powers player positions on the CAD map, unit proximity (Live map), commands to the server from Moderation → Console (Moderation) and the player count of sessions (Sessions).
The card shows the status: no key, set and working, or set but not responding. If it does not respond, those features switch off.
The key never leaves the Blixye server: the client does not receive it to talk to ER:LC.