The Re-Direct URL is set here as below via Dashboard > Lists > Your List > Overview > Pages > Dropdown list top right hand corner > Subscription Confirmed > Re-Direct URL
You then choose whether to display the “Subscription Confirmed” page/message (nothing to do with Double Optin Confirmation) or Re-Direct to your Welcome page on your website, or any other web page.
The content of the “Subscription confirmed” page can be edited, or the Re-Direct URL added, as below.
Should you wish to redirect a subscriber who is already in the List, then you can set that as below. Those already in the LIST will be the ONLY the only one’s redirected if this second redirect URL is entered as below. IF you wish, that URL CAN be to the same page as the one for new subscribers.
SO – do NOT set that re-direct if you want new Subscribers to be re-directed.