Your available funds are saved in BUSD, this is a stablecoin that is equal to the US Dollar.
We show the available funds in Euros because this is the currency that is most recognizable for our users. So it is possible that your amount is fluctuating with the rate.
As an example, if you have €100 in your available funds. This can change to €99,xx or to €101,xx depending on the fluctuation of BUSD in comparison to Euros. This can happen by the minute or in some cases even seconds. Rest assured that you will continue to have the same amount of stablecoin in your available funds until you yourself take action.
You can see the amount you have in the stablecoin in your assets. Go to menu More > Your assets.