libcurl, enabling chunk encoding with multipart form data - c++

Question

What i want to achieve is to be able to upload a file of any size and also send post data in the same request. The server is guaranteed to be able to handle chunked encoding and also support unlimited size of size.
To achieve that I used CURLOPT_HTTPOST and set the header Transfer-Encoding: chunked, The problem is that I'm am not sure if libcurl is actually using chunked encoding at all. In my attempts to try and figure out I set CURLOPT_VERBOSE to 1 and implemented a custom debug callback to monitor the http headers. From curl I can only see 1 HTTP Request and only 1 HTTP Response (code 200). I didn't see any http code 201 responses.
My question is how do I enable chunk encoding for file uploads in multipart POST requests? If what I'm doing is correct why does libcurl not show me all the requests, how do I make sure it works like it is required?
Bellow is a short example of what I am doing in code.
//Assume `curl` has been initialised
struct curl_httppost *formpost=NULL;
struct curl_httppost *lastptr=NULL;
struct curl_slist *headerlist=NULL;
curl_formadd(&formpost,
&lastptr,
CURLFORM_COPYNAME,
"foo",
CURLFORM_COPYCONTENTS,
"bar",
CURLFORM_END);
curl_formadd(&formpost,
&lastptr,
CURLFORM_COPYNAME,
"file",
CURLFORM_FILE,
"filepath",
CURLFORM_FILENAME,
"filename",
CURLFORM_END);
headerlist = curl_slist_append(headerlist, "Transfer-Encoding: chunked");
curl_easy_setopt(curl, CURLOPT_URL, "https://foo/uploadfile");
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerlist);
curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, curl_write_to_string);
curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, curl_progress_cb);
curl_easy_setopt(curl, CURLOPT_XFERINFODATA, &progress_id);
curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);
curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 1);
CURLcode res = curl_easy_perform(curl);
Thanks in advance