Read this (quote from changelly):
Changelly’s trading algorithm is integrated into the largest cryptocurrency exchange platforms, including Binance, Poloniex, Bittrex etc. In the span of milliseconds, Changelly makes bids and asks on the platforms, then selects and suggests the best available rate and displays the estimated rate on our site. The rates remain approximate until the transaction is actually made on the blockchain. The exchange rate at the time of a transaction may differ slightly from the estimated rate that you see when you begin a transaction.
This should be moved to Service Discussion.
