The ETH fee in the transaction is 100% OPTIONAL. It allows you to buy a small amount of ETH (Ether) from PayTrie to help you transfer your stablecoins out of your wallet in the future.
This is particualarly useful for new wallets that currently don't contain any ETH. Without ETH, your stablecoins will remain stuck inside your wallet as you are unable to pay for the transactional cost to move the stablecoins.
PayTrie uses the current gas price to estimate how much is required to send 1 ERC-20 transaction. From there, we provide a marked up price to cover the transactional cost it would require for us to send you the ETH. This feature is simply for convenience and should not be used as a method to buy and invest into ETH.
NOTE: If you are sending the stablecoins to a Centralized Exchange, you do not need to add ETH to your transaction.