In order to trade ETH on Radar Relay, you will first have to wrap it.
Why do I need to wrap my ETH to trade?
For the time being, relayers can only trade ERC-20 tokens. The ERC-20 standard was created after Ethereum was made so ETH doesn't conform to it. In order to make it meet the standard is must be "wrapped".
All wrapping and unwrapping of WETH is done directly with the WETH contract and is not a trade over the 0x protocol. Wrapping and unwrapping are always 1:1 functions and there is no market impact or slippage. In RELAY this action is available under the Trade function and in RELAY classic it is accessible in the wallet drawer.
Never send tokens directly to the WETH contract. Always use the wrapping and unwrapping functions.
For more information on WETH and why it's needed visit WETH.io
How to wrap ETH - RELAY
In the RELAY app select Trade https://relay.radar.tech/
In the I want to trade card select ETH
In the I want to receive card select WETH
Connect your wallet
Input the amount of ETH you would like to wrap (or the amount of WETH you would like to receive)
Click the Trade Now button and confirm the transaction with your wallet.
How to wrap ETH - RELAY Classic
RELAY Classic https://classic.relay.radar.tech/
Open the wallet drawer and make sure you're on the Your Tokens tab.
In the field under ETH enter an amount of ETH you wish to wrap
Make sure to leave enough ETH unwrapped in order to pay for transaction fees. They can't be paid in WETH.
Press the WRAP button, choose your gas price and then confirm the transaction on your wallet.