By default, WP Travel plugin sets the Trip slug base to ‘itinerary’. Due to this reason, your-site-name/itinerary page shows the trip archive and list all the trips.
Case that your archive page is giving the 404 error may be because you have set the Trip base to some other slug than itinerary. You can verify this case by going to Admin Panel > Settings > Permalinks > Trip base
In this case, your archive page will have the URL site-name/custom-text in Trip base
*Note – If you do not have any trips created in your site, you will get the message “Trips not found” in the archive page.