If you receive an error when trying to enter a withdrawal address this could be one of a couple
You may have an old or blank address "locked" in, to change this just enter your 2fa (OTP) code and select "unlock address." You will need to wait 24 hours for your address to unlock, then you will then be able to enter a new address.
If the error is saying "Invalid bitcoin address", please make sure you are entering a valid Bitcoin address, not a wallet ID.
Some browsers will automatically fill in your username in the address field. If this is the case please try a different browser or disable your password manager.