Expression Engine 3 won't show up in Iframe or Facebook Page

Weird behaviour Test <IFRAME> at https://www.itsmysystem.com/facebook/

Note the EE site at https://www.itsmysystem.com will not show up in this iframe.

The site will also not show up on a Facebook Tab (this is what got me looking into this). Does anybody know what is going on or can help?

My v2 Facebook sites have no issue as an IFRAME or Facebook Tab

Virgil…