If you are using 2FA with SMS text messaging, the verification code expires after three minutes. If you didn't enter the code quickly enough, it will be rejected. Click "resend," and try again. You may only request 5 codes within one hour.
If you are using 2FA with an authenticator app, the verification code expiration will vary based on the app you are using. If the first code you try is not accepted, wait for the app to generate another and try again.
If after a few attempts you still can't get in, contact your portal administrator for assistance in resetting your two-factor authentication.