Every time you send or exchange crypto in the wallet you need to pay the network fee to fuel the transaction. This fee goes to miners who confirm it in the blockchain.
The fee itself depends on the network load and the difficulty of the transaction. If there are a lot of transactions at the moment miners will confirm more expensive ones first.
You can check and change the network fee while sending crypto in the “Fee” box. You are free to change it and set it lower/higher manually, though it has its consequences. For BTC and some coins, it may take a lot of time for the transaction to be confirmed if the fee is insufficient.
We suggest our users choosing the recommended fee for their transactions not to fail. Custom fee is available for advance users. Using custom fees may result in more time to confirm, we do not recommend using it if a transaction is time-sensitive. Before choosing and confirming it, check the network load.