I uploaded the files to FTP but this error?

it means; Your connection is not safe

my site adress is http:// but when i install the flarum my site changing to https://

error its SSL error. I have not SSL :/ beta 6 is working but beta 7 why problem?

When i uptade i get this but i installed from zero, and upload the database its not problem

Edit your config.php and change the url value.

Also check your sites available nginx config for your site if you used SSL at any point in time,