Embedding a list of Discourse Topics in another site

[david (David Taylor)]

Most likely related to this change: (cc @falco)

CSP Frame Ancestors enabled by default

We just enabled the Content-Security-Policy (CSP) frame-ancestors directive by default on Discourse. By default it allows self and any domains allowed in Admin > Customize > Embedding. If necessary, a site administrator may disable it using the site setting content security policy frame ancestors, but that is not recommended.

Do you have your main site registered under Admin > Customize > Embedding?