If you are doing WinSock TCP stuff you need a “header sandwich” to instruct Unreal to ignore all the Windows base stuff.
// put this at the top of your .h file above #includes
// UE4: allow Windows platform types to avoid naming collisions
// must be undone at the bottom of this file!
#include "AllowWindowsPlatformTypes.h"
#include "prewindowsapi.h"
… your
… header
… file
… content
// put this at the bottom of the .h file
// UE4: disallow windows platform types
// this was enabled at the top of the file
#include "PostWindowsApi.h"
#include "HideWindowsPlatformTypes.h"