custom error for restricted SFU config error

locales/en/app.json

@@ -94,6 +94,8 @@
     "matrix_rtc_focus_missing": "The server is not configured to work with {{brand}}. Please contact your server admin (Domain: {{domain}}, Error Code: {{ errorCode }}).",
     "open_elsewhere": "Opened in another tab",
     "open_elsewhere_description": "{{brand}} has been opened in another tab. If that doesn't sound right, try reloading the page.",
+    "room_creation_restricted": "Failed to create call",
+    "room_creation_restricted_description": "Call creation might be restricted to authorized users only. Try again later, or contact your server admin if the problem persists.",
     "unexpected_ec_error": "An unexpected error occurred (<0>Error Code:</0> <1>{{ errorCode }}</1>). Please contact your server admin."
   },
   "group_call_loader": {