Hi Gautam
Subtype and Field name is not required. Are you getting any error when you execute this or simple nothing happens? When I had tried this in my system for the action type and reason that we have, it was working perfectly. Just recheck if you have taken the correct action type and reason values. Also, check if your id has authorization to create infotypes in the background. There was another query like this a couple of days back where the consultant discovered that he did not have the correct authorzation and thats why the dynamic action wasnt working in the background (Delimit IT0105 through background while doing PA40 action)