Http request post api call for multiple documets

How to send multiple (uncertain) number of document in a post Http Request web api activity ? This api call response with a transaction id, so I get one transaction id for each call if I send one document from those uncertain number of document. I don’t want to do that. I want single transaction Id for all the documents. I have gone through this thread
Http Request but there is no solution. Since the thread was old, I am creating this new thread to find the answer. Kindly share any method to resolve this issue.