Don't fill in anything just click payment to faucet box above the text field.
Logged by email, and i not fill address, press Withdraw Balance to Faucetbox and see error "Invalid 'to' address."
you used a email for login !!
so you cant pay to faucetbox when your wallet is an email !
but you can cashout your balance to any xapo mail !
on the login page you see:
Enter your Faucetbox Adress or XAPO Mail here and start to claim!