You should not need to use the DVR.
Just enter the url into the "Enter (or Drag and Drop) the URL of a video page to DVR)" and hit enter.
You can enter your cable credentials if they are adobe pass ones via Settings > Internet Downloads > Advanced Settings > Extractor Logins, if the video is only available to registered users.
Testing the DVR on history.com works fine here.
If you really want to use the DVR and are stuill having issues then please provide debug logs as per:
I'm using the DVR function and logging into History.com with my cable account. I'm not getting video, just audio!