Cannot publish DirectQuery composite model to a SharePoint Workspace - PowerBINotAuthorizedException

I seem to have an issue where I can publish regular models just fine, but I cannot seem to publish a composite model.

Half of my model uses DirectQuery from a separate model that a 3rd party we've hired has made. The other half of my model uses a group of queries that I've built upon folders of CSVs and Excel files. When I go and publish this to , I am greeted with the following error:

If I try to publish the composite model to "My Workspace", the publish is successful but when I open the report in the browser, half of the tiles have this error:

And at the top of the report in "My Workspace", there's this error visible as well:

I've tried sharing the 3rd party dataset with both myself, as well as the e-mail address associated with the sharepoint workspace, in case that was the issue. That didn't seem to fix it.

I've also tried manually importing my PBIX file on the , but I got this error saying it couldn't import the data.

After closing this error, the dataset and report are not there, but the dashboard it. Clicking on the dashboard, it just tells me Permission Required