I see that it’s not possible to embed comments from a private forum (on a site that uses a separate domain):
What a colleague is using for comments on a Ghost site though is a public forum (on a completely different domain), publishing mostly free posts. He’s recently published his first members-only post, and as I switched its associated topic on Discourse over to a category where it’s not viewable by “Everyone” but rather to a particular Group (associated with paying members on the Ghost site), the embed now displays the message “Error Embedding”.
Although the OP said that private forums (on separate domains) won’t allow the embed to work, this is a public forum but with a private category. Is the problem I’m seeing due to a private category on a public forum functionally being the same as a private forum? I did after all read the following comment, which seems to back up that assertion:
If it is the case that topics from private categories on public forums can’t be embedded out of the box, is there any way that this could be done with some adjustment of the embed (and/or the platform)? I’m not in any major rush to (hopefully) “fix” this issue as I’m somewhat okay with temporarily setting the private category to public (as Discourse can’t scrape the private Ghost post and thus inadvertently display its content to non-paying users on Discourse), but if getting this to work is possible I wouldn’t mind hiring somebody at a later date to amend the embed and/or put through a PR for the platform.