So you are trying to exchange BNB to BTC?

Do you see the error under BNB box when trying to convert them from BNB to BTC?

It means that if you want to convert them into BTC you need a minimum of 0.05BNB you only have 0.01853403BNB so it won't work to convert them directly.

If you want to exchange them into BTC I would suggest you go to trading classic or advanced to exchange them or exchange BNB to USDT/BUSD then buy BTC.