To execute a smart contract, you’ll have to pay a “gas” fee. This fee goes to the network and is used to reward the participants (known as miners or validators) who process your transaction. This gas token is usually the native coin of the blockchain. For Ethereum, it’s ETH, for Solana, it’s SOL and for Avalanche, it’s AVAX. The only notable deviation to this is blockchains on the Cosmos ecosystem (called appchains), which operate independently from one another; there is no “official” coin on the Cosmos ecosystem, and a decentralized exchange might be powered by the native cryptocurrency issued by that exchange.