Are you referring to the 6-digit filing verification code near the end?
Is the code coming by email? If so, you have to leave that original screen open that asks for the code while you go to retrieve the code. You have to use a second window or a second browser tab to go to your email to get the code, and then enter it in the original screen you left open. If you close that first screen, the code will always be seen as invalid or "expired." Another option, if you have a smartphone, is to leave the first screen open, then use your phone to retrieve your email.
Also see this FAQ:
FAQ: What if I'm having trouble with my filing verification code?
https://ttlc.intuit.com/community/security/help/what-if-i-m-having-trouble-with-my-filing-verificati...