I believe showOpLikes should only work when sorting by OP likes by visiting a URL like https://meta.discourse.org/latest?order=op_likes, otherwise the op_like_count isn’t included (showLikes, should work… but that’s the total for the entire topic).
You can see this in action by viewing https://meta.discourse.org/latest.json and https://meta.discourse.org/latest.json?order=op_likes… op_like_count is only available in that second link.