It looks like that's just a generic error message. For me, this websocket message is received when the error appears:

    {"error":true,"body":"Your credit balance is too low to access the Anthropic API. Please go to Plans & Billing to upgrade or purchase credits.","done":false,"id":"XXXXXXXX","type":"cf_agent_use_chat_response"}

The error message should point that it's the server, not the user problem.