Binance - Trailing stop

Hi guys, Does anyone know how to set a trailing stop on binance futures? Once the trade has been opened and I go to the TP / SL tab on my trade there is an option for trailing stop. I set my activation price and the SL % but when I tested it my SL that should have been hit didn't. I also can't figure out how to set it when opening the trade. YouTube hasn't been any help! I'm also using mobile if that changes things. Thanks