Crypto assets can be divided into two groups: coins and tokens. Coins have their own blockchain, while tokens are built on existing blockchains. As a rule, coins are used for paying fees because they serve as the native currency within a specific blockchain network. Using coins for fees simplifies transactions and ensures a uniform currency for the network's operations. Tokens, while versatile, may have varied values and use cases, making them less standardized for transactional fees.
If you send a token which is not a native coin for a certain blockchain, you are required to pay a fee in the native coin. For example, if you send USDT via TRON, you have to pay a fee in TRX, which is a native TRON coin. That is why you always need to have TRX on your wallet to execute such transactions.
USDT (Tether) is a token which can be referred as a stablecoin since it offers price stability as it is pegged to a fiat currency. There are several networks that support USDT: Avalanche, Ethereum, Polygon, Solana, TRON, Binance Smart Chain, Arbitrum, Gnosis, Optimism and others.
If you don't have enough coins to pay a fee, you will get such a warning when sending cryptocurrency:
To purchase the necessary coin, you can buy it via our service or receive it from another wallet.
The list of all the supported blockchains and native coins:
Bitcoin - BTC
Ethereum - ETH
TRON - TRX
Polygon - MATIC
Optimism - ETH
Binance Smart Chain - BNB
Arbitrum - ETH
Litecoin - LTC
Fantom - FTM
zkSync - ETH
Solana - SOL
Avalanche - AVAX
Linea - ETH
Gnosis - XDAI
Note that the native cryptocurrency should be on the same network on which you pay the fee. If you're paying the fee on Optimism, you should have ETH exactly on the Optimism address.