Failed to subscribe to events using rpc: suix_subscribeEvent

I am getting this error: "error": "{\"code\":-32602,\"message\":\"Invalid params\"}" when I subscribe to the events from websocket connection. The json encoded message sent on websocket connection is: {"jsonrpc":"2.0","id":1711950855951,"method":"suix_subscribeEvent","params":[{"Package":"0x65ac3137937ba87148ce88b9e6dbe33d17bd1ab59881171d11836a8897a396be"}]}.

Note: this RPC api was working fine a week ago but since few days, I am getting this error.