Subdomain vs Folder?

I’ve installed mautic in a sub-folder called “/mautic” and discovered that all the links in my emails are not redirecting. They have the URL:

e.g.

site.com/r/dfvanojkefawe89fg394hfnrf - which goes to a 404 (the long string of character I just made up to give an example URL)

When I amend the URL to site.com/mautic/r/dfvanojkefawe89fg394hfnrf - which goes to a 404 it redirect fine.

Is there a way to fix this in Mautic? I did make a mistake when installing by putting Site URL as

site.com/mautic

and changed it to just:

site.com

Could that be the issue?
I also read on another post about “rewrite rules” but have no idea what these are?

I don’t get this issue on another set up which is on it’s own sub-domain, but really don’t want to move the installation to its own sub-domain to get this to work.

Any suggestions to fix?