When I navigate to the Meta Business Suite and then the Events Manager, I'm getting the error in the attached image after clicking 'Open event setup tool' under my pixel's settings and then 'Open Website' for my domain.

My application is a react app running on Heroku, with Cloudflare DNS. I'm getting the same error when I paste in the Heroku app url (not just for my custom domain name) which would suggest this is an application-level issue. Although I wasn't able to add it to an allow-list because of Heroku's domain prefixes, I still think the issue is properly isolated. For safety I've regularly purged my Cloudflare cache.

It is also worth mentioning that I've tried clicking 'Open Website' for various permutations of my domain name (with https, www, etc.).

I've added the pixel to my application following these instructions: https://www.youtube.com/watch?v=4opaiqpKpeQ

and also within my index.html in an attempt to have it as part of the static web content.

What happens when I click the 'Open Website' button is a very opaque process. From the network tab it seems to be a simple redirect, but I'm not sure what prevents Meta's tooling from accessing the pixel? Does it have to do with CORS?

The issue is very much particular to what is happening when I click this button because the Meta Pixel Helper shows that it finds my pixel and the PageView event is firing on the custom domain and Heroku link.