Browser cache not working in subdomain

I have a problem with the cache on my staging website. I have already tried to disable/enable all the plugins plus the mod_expires module is installed. I have the same website in the same machine with the same php version and plugins and it works. The problem seems to be from the fact that it's a subdirectory website.
this is the error i see in the browser cache tab:

Browser Caching is not working properly:

- Your server may not have the "expires" module enabled (mod_expires for Apache, ngx_http_headers_module for NGINX)
- Another plugin may be interfering with the configuration
If re-checking and restarting does not resolve, please check with your host or open a support ticket with us.