I’m having a problem with a Facebook App I added to my Facebook Page it no longer works because of new CSP rules

I’m having a problem with a Facebook App that I added to my Facebook Page. It no longer works because of new CSP (Content Security Policy) rules.

The app is basically a framed page served from the sites.google.com domain, it worked for many years but seems to have stopped working some time around May this year, i think due to the Chrome browsers changing their CSP policies.

When i try to view the app on Facebook, it just displays a grey square where the page content should be that shows the error message “This content is blocked, contact the site owner to fix the issue”

I am the site owner, but i have no idea how to fix it. Does anyone know of a way around this problem, i.e displaying a Facebook app which consists of framed content from another site on your Facebook Page?