To view request headers of incoming requests from IIS, you can use failed request tracing in IIS to include status code 200. This would log successful requests too and you can view all request headers in the "request details" > "general request headers" section.
Here, I received another SharePoint 2013 workflow error. This time the workflow was not able to send emails and the following error was being shown Retrying last request. Next attempt scheduled in less than one minute. Details of last request: HTTP Unauthorized to http://sitename/_vti_bin/client.svc/web/lists/getbyid(guid'guid') Correlation Id: id Instance Id: id Fortunately I came across this post which gave me the answer http://sharepoint.stackexchange.com/questions/89101/failed-to-retrieve-the-com-class-factory-for-component-with-clsid-sp-sprequest Solution 1: In InetMgr, go to advanced settings for Security Token Service Application Pool and change "Load User Profile" to true. Recycle application pool. Reason 2 and Solution 2 : There could be another reason for this error. The workflow authentication can fail if the user executing the workflow (this will be the user initiating the workflow) is given permission through active directory group and the co