You are moving to Evessio and you have old links
It is likely that your previous websites had URLs in a different format from Evessio. Here are some best practices which you should always do when creating new events on Evessio
1. Update Google search console
Search console: https://search.google.com/search-console/about
TIP: If you need to authenticate your event website the easiest method is to add your Google Analytics or Tag Manager code via EVENT > Settings
Most organic traffic is likely to come from Google and updating the domain and its URLS is easy via Google. Evessio automatically generates sitemaps to facilitate an up-to-date view of published URLs for a site - you can find the sitemap for any event here e.g.:
https://clientdemo2020.evessiocloud.com/bespokeclientdemo/en/sitemap.xml
>> Sitemaps are automatically re-built when new pages are linked to in menus or page content

Every domain also has a robots.txt file (read by search engines) automatically generated which will reference the sitemaps of all published sites on the domain e.g.
https://clientdemo2020.evessiocloud.com/robots.tx

Sitemaps are visible via the SEO tab in the pages admin area:

2. Build a 'friendly' "page not found" page
- Each event has this system page where you could build a list of useful links or downloads for the current event. Use a "General content" content type to create your list of links.
- Users landing on this page can them make quick choices about where to go next
