This id is reserved for the built-in local storage server
Admin create server returned 400 because the id is reserved for local.
Why this happens
Client tried to create another server with the built-in local id. Local already exists and is protected.
Diagnose and fix
1. Create remote/CDN servers without specifying the reserved local id (let the UI assign ids).
2. Edit the existing local server instead of recreating it.
3. See Manage the local storage server.
4. Related: servers already in trash may need restore first (Phase 55).