The Refund Address can be set in the transaction settings under the "Refunds" tab. The Refund Address is the address that funds will be sent to in the case that a cross-chain transaction fails and funds need to be returned to the user.

If you are interacting with Superform through an EOA there is no need to set this because your address is the same on every chain. If you are interacting through a contract account such as a multi-sig where you may not control the same address on every chain, you should set the refund address in case the transaction fails and you need to be refunded.
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