Mexy I'm really not sure what it could be.
I notice there's a little orange icon with 2 arrows next to the URL in the error message, but I don't know its meaning. Could it mean that an HTTP redirect was performed during that request? There might be more information visible in the Network tab of the browser tools.
I don't see the public
part in the error message in the video, however I see your browser tried to auto-complete the forum URL with /public
, so I assume you must have changed the URL after installation? If the problem happens with multiple browsers it might not be a browser cache issue, but maybe there are still redirects setup incorrectly on the webserver itself?
If nothing helps and seeing you don't have a lot of content in the forum, you could try performing a full re-installation (make a backup first so you don't loose any of your work!). Delete the virtual host in your server configuration, delete the Flarum folder, clear your browser cache for the domain and start over. Make sure to setup the correct URL before following the Flarum wizard.
After performing a full re-installation if it works you could then swap the database with a backup of what you had done in the current version and if it still works you'll have lost nothing apart from the avatars, which can also be copy-pasted from a backup.