It's the usual setting up custom domain steps. There are some instructions at Options>Application>Change domain name on your forum. You need to go to your dns records and set a cname record pointing a subdomain to (in your case) n7.nabble.com. The domain should redirect to the Nabble homepage if configured correctly. Then set it on the change domain page.
You can still access your site to do this. On Chrome, click on the shield with a cross in the right side of the url bar, and click load unsafe scripts.
Let me know when you've done that and then I can set up the https on our side.
I'm going to try posting again here and see if I can get a response this time.
How do I get my forum to embed within my https site?
It sounds as though there is a solution now. Is this correct?
It sounds as though I need to setup https on my own site (done, https://training.aealearningonline.org), and that https has to be set up on my forum (nabble.aealearningonline.org). If that is the case, how is that done? Is this something that Raven is doing for groups?
The forum I've used in testing does not work if the embed links are not https, it just shows a link, like Flick's site.
The 404 issue appears to be a different problem, some generated urls look wrong. Probably a fixable bug.