The service charges a fixed fee for exchange operations - 1% of the transaction amount. In different periods, the fee may be either $ 0.01 or $ 1, and sometimes it changes at the time of confirmation of the transaction.
At the same time, the rate may differ from the one that you fixed on your exchanger, as the data is updated very quickly.
Broex has nothing to do with these surges - they are caused by the volatility of cryptocurrencies.
Volatility is an indicator of the variability of an asset's value over a certain period of time. High volatility means that the asset changes in price very often. This behavior is typical for the cryptocurrency market.
It is not always possible to predict price changes. Remember how Bitcoin sagged after Elon Musk's tweets or Chinese sanctions - the change is almost instantaneous. During the exchange, the service processes the data of hundreds of platforms to find the most profitable rate, and if it suddenly increases or decreases, the amount of the fee will also be different.