Can’t access 2nd site (sub) dashboard of WordPress Multisite

I can’t access the dashboard of the second site. When I go to the second site, I only see the HTML page without the style (css).

When I try to access the dashboard (from Safari), I get this message from the browser: “too many redirects occurred trying to open”.

Subsite set-up

example.com (works)

example.com/secondary (doesn’t work)

I tried disabling all plugins and change to the default theme. It still doesn’t work. Here’s what in my .htaccess file:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

</IfModule>

# END WordPress