You don't explain what you have tried. The URL of your main site would be helpful too, so we can see what code you have inserted there.
Have you gone to OPTIONS > EMBEDDING OPTIONS and copied the code fragment you find there and pasted that into the source code of your main site.
The code that appears there will take the general form:
Forum Name<script src="http://yourforumname.123456.n1.nabble.com/embed/f1234567"></script>
We should be able to see your version in the source code of the page in which it is embedded on your main site.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.