Register-SPWorkflowService Failed to query the OAuth S2s metadata error

Scenario: 

You have followed all the specified TechNet requirements/permissions in setting up SharePoint 2013 and Workflow Manager 1.o farm but when Registering Workflow manager with SharePoint site collection you might have got the below error:

Register-SPWorkflowService : Failed to query the OAuth S2S metadata endpoint at URI ‘http://xxxx/_layouts/15/metadata/json/1’. Error details: ‘An error occurred while sending the request.’. HTTP headers received from the server – ActivityId: 5b035802-7a59-4235-acb5-943a0e21e942. NodeId:
xxxx. Scope: /SharePoint. Client ActivityId : 66bd6434-9778-4a6f-b275-63a399d73c8c.

Solution:

Basically it is trying to connect to the SharePoint url end point (http://xxxx/_layouts/15/metadata/json/1 . In my case the SharePoint url (which has host header) was not accessible from Workflow Manager server (as I have not dns published the url). I added the SharePoint url to the Workflow manager server host file and can access the SharePoint url.

Now the Register-SPWorkflowservice command runs without issue.

Key here is that make sure that both SharePoint and workflowhost urls are accessible from the SharePoint / Workflow Manager server.

Hope this helps.