Identify replies in Microsoft Search API search Teams messages response

Using Microsoft Search API to search Teams messages, how do I tell if a hit is a channel message (post) or a reply to one? They look exactly the same in the response.

Adding the field "replyToId" to the request doesn't add it to the response. I can't see any difference between the hits.

Currently, after getting the search response, my code calls the API's get-message to get the data of each message, but it fails for messages that are actually replies.