One more : "Floating price. The final Bitcoin amount will be determined at the time of the trade finalization."
Let's say I want to buy BTC for 1K€ in cash. I will know my price (amount of BTC), at the moment I give my cash to the seller?
If the option is not checked the exchange rate for the trade is determined at the moment you open the trade. If you are buying Bitcoin you then have an X amount of minutes to send the payment to the seller. This can be anywhere between 30 mins - 3 hours or more. No matter what happens with Bitcoin in that timeframe (if it goes to $20.000 or drops to $200) the trade will still go through according to the exchange rate that was determined when you opened the trade.
If the Floating price option is ticked the exchange rate will be determined after the seller confirms receiving the payment and once the Bitcoins are about to be released and not like in the example above when the trade was started. This means that the exchange rate could change depending on the current Bitcoin vs USD exchange rate.