Make sure your site path does not include a forward slash (/), as this will cause the server to treat it as a subdomain and prevent the site from loading correctly.
Update the site path
Find the site under Direct Debits in eDD.
Click the Actions dropdown next to the site.
Select Change Information.
Edit the Site Path to remove any forward slashes (use hyphens if needed).
Click Next through the setup pages.
Select Save on the final page.
Once updated, the preview should load correctly.