What will be 2nd parameter of HttpAddRequestHeaders if I want to send a TEXT file to server?

I want to send a text file to a server. One php site will receive this text file on the server side. Can anyone tell me what will be lpszHeaders,2nd parameter of HttpAddRequestHeaders in this case?
 

BOOL HttpAddRequestHeaders(
  _In_  HINTERNET hRequest,
   _In_  LPCTSTR lpszHeaders,
  _In_  DWORD dwHeadersLength,
  _In_  DWORD dwModifiers
);
 

 
Thanks