Websocket not working in sandbox (The api key is not valid or does not have access to this subscription.)

Hello,

I'm trying to connect to a websocket, using sandbox credentials but I'm always getting a "The api key is not valid or does not have access to this subscription." response.

I'm using the same key, after connecting I send the key as it is, something like:

await ws.SendAsync(Encoding.ASCII.GetBytes(apiConnection.AccessToken), WebSocketMessageType.Text, true);

Is this a sandbox thing?