Configuring Workflow Manager with SharePoint over HTTP

Hi,

I have installed workflow manager on a dedicated workflow server.
I have also installed SharePoint 2013 on its own server on the same domain.

Whenever I reach the workflow registration step (over HTTP), Register-SPWorkflowService, I get the error:
Failed to query the OAuth S2S metadata endpoint at URI '.../_layouts/15/metadata/json/1'.  Error Details: 'An error occurred while sending the request.'

If I open the URI, IE will ask me to save or open the json file.

Using Fiddler I can see that the URL http://[wfserver]:12291/SharePoint/ is requested and that the response 404 Not Found was returned with the error ScopeNotFoundError Scope '/SharePoint' was not found. ScopePath/SharePointEntityName/SharePoint

Any idea what is going on and how can I solve this?

Thanks.