Invalid Security Token when trying to login

I've recently moved my grav website from the root hosting folder to a subfolder and adjusted the .htaccess accordingly, based on siteground's suggestions. Once moved, all links had the actual subfolder name showing up. eg. www.domain.com/subfolder/blog instead of www.domain.com/blog. I saw a setting that may resolve this issue in system.yaml called custom_base_url, which I set to be only http://www.domain.com. Now the menu links show up correctly. However, when trying to login to the admin, I get invalid security token. I followed all the suggestions on this page but to no avail.