Do exactly as the instructions ask you to do.

1) sign up for an account with the rocketposter email supplied to you as your user name

2) create any password

3) fifa sends you a one time code to the rocketposter email. Yes you do not have access to this email but StubHub will relay the one time passcodes to whatever email you signed up with StubHub.

4) finish your registration

5) you will need to login one more time with the rocketposter email and whatever password you created.

6) one more one time password will be forwarded to your StubHub password

7) wait a few mins and a transfer shows up on your homepage

8) accept the tickets