How to request Mark Price using Websocket?

I am making a request with:

{"method": "SUBSCRIBE", "params": ["btcusdt@markPrice"], "id": 4}

However, it returns nothing. If I try the same call with “btcusdt@aggTrade”, then it starts retrieving prices for Aggregated Trades, but for Mark Prices, it does not work. What am I doing wrong?

no issue for me to get markPrice.