Transaction Fee's
Like all traditional decentralized Crypto Wallets, all transactions incur a network / transaction / gas fee, payable in the native token of the network on which you transact.
On the Ethereum (ERC-20) Network, that token is ETH, and every outgoing transaction (Send or Swap) will require a certain amount to be in your wallet to cover the fee.
On Smar Chain, that token is BNB, and it works the same way as ETH.