Y’ALL swaps happen on Base. If your ETH is sitting on Coinbase, send it out through the Base network. If it is parked on Ethereum Mainnet, bridge it over and leave a little ETH behind, because even a good truck needs gas to start.
From Coinbase, pick Base as the network and send ETH to your own wallet. Your wallet. Not the token contract. Not some ditch address Bubba found on a napkin.
Bridge ETH from Ethereum to Base, wait for confirmation, then come back to the swap window. Cheap gas lives on Base. Mainnet charges like it owns the marina and the sheriff.