If during export bookings to .ics feed at the WP Booking Calendar > Settings > Sync > "Export - .ics" page you have 404 error, then check these steps:

1. Go to: WordPress Settings > Permalink page. Please be sure that you set for "Permalink structure" option "Post name" instead of "Plain" value.
2. Recheck that you have correctly configured .ics feeds URLs for exporting. Open WP Booking Calendar > Settings > Sync > "Export - .ics" page and be sure that you have specified URL for exporting .ics feeds with one level of depth. For example: https://server.com/ics/my_resource/ or if its not work try to set it as this URL: https://server.com/ics/my_resource/wpbm.ics
3. Please double-check the root folder of your website for any .htaccess files. Make sure these files don't have security restrictions affecting link generation. It's a good idea to reach out to your hosting support for assistance, as they are more knowledgeable about potential security restrictions.
4. Take a look at any other security plugins in the WordPress > Plugins menu that might be blocking the creation of the URL structure for the .ics feed. Try deactivating each active plugin one by one and test after each deactivation. If the issue persists, deactivate all plugins and switch to the default WordPress theme. Test again to see if this resolves the problem.
5. Review your server's error.log for any related errors in your server configuration. If you can't locate the error.log file, contact your hosting company's support for assistance in finding this file.
6. If the previous steps don't resolve the issue, it suggests there might be server configuration restrictions. In this case, only your hosting support or server administrator would know how to reconfigure your server to avoid blocking the generation of the .ics feed. Please inform your hosting support that the "wpbm.ics" file is not a physical file on your server; the script generates it on-the-fly when someone attempts to access the URL defined in WP Booking Calendar > Settings > Sync > "Export - .ics" page.

   Please note, Booking Calendar generate virtual ics feed form the php script. So it’s not the real file at that folder. It’s generate such feed dynamically, when someone access such url.

   System have to work in the same way as WordPress working with pages at your website. As you may know, you can have link to some page like this: https://server.com/category/some-page/ . But it does not mean that you have real file like category/some-page/index.html at your server. Your system access general index.php file at root of your website and then load specific page based on permalink structure. The same with .ics feeds in Booking Calendar, when server try to access url: https://server.com/ics/wpbm.ics
   this .ics feed generate dynamically from the php file.