Hi Piyush,
postFeedElement(communityId, feedElement, feedElementFileUpload)
The ConnectApiHelper class currently doesn’t support taking a ConnectApi.FeedElementCapabilitiesInput as a parameter when posting a feed item. You’d need that in order to use a ConnectApi.PollCapabilityInput. You’ll need to either avoid using ConnectApiHelper, or modify your copy of it so that it takes in the additional parameter.