Changelly is a 3rd party instant exchange service that works with exchanges like Bittrex, Poloniex, and others. Changelly offers the best available rate at the moment the transaction is completed and charges a 0.5% commission fee on top. "In case this is your first exchange, Changelly will provide a fresh Ardor deposit address, therefore your transaction will need to cover the 1 ARDR fee to create this new account, which means, your Ardor fee should be 1.01 ARDR [or] your Ignis fee should cover 1.01 ARDR based on the current bundling rate. Subsequent exchanges from the same wallet should use the same Changelly deposit address so only needs to cover the 0.01 ARDR transaction fee" (source). Nxter.org is not liable to any problem encountered with the Changelly exchange service. Their website.