You're not supposed to place the the public address though. in the second box you're supposed to place the private key
that the OP sends you upon completion of your custom public key. In the top box you place the private key that you were asked to save during step 1.

Nevermind I see that it states that it can accept the public key. That's weird because I didn't generate the private key for my public key address using the public key itself in the second box.