The only places where documentation exists currently is the old and now read-only community post (https://community.cisco.com/t5/security-knowledge-base/ipsk-identity-pre-shared-key-manager-portal-server-for-ise/ta-p/3904265) and the iPSK Manager Git...

"Warning: Trying to access array offset on value of type bool in /var/www/iPSK-Manager/portals/index.php on line 104" is going to be a cosmetic message in the log since the SAML setting is probably not set.  It isn't going to cause things not to work...

This article does a very good job explaining the different COA options and configuration around COA in ISE if you have not seen it. https://www.linkedin.com/pulse/ise-profiler-radius-coa-part-3-reza-alikhani-4sycf

What are you using for the URL for the portal and what type of portal did you choose?  The portal pages work differently than the admin portal page and you need to format the URL properly otherwise the page will generate a 404 error which it sounds l...

@zhenningx Redhat should be fine, it just hasn't been tested, but as long as you followed the setup items in the README for Apache, MySQL, PHP, it should be fine.  If you got through the installer of iPSK Manager then its a pretty good sign you did a...