This worked for me:
#include <SocketSubsystem.h>
#include <IPAddress.h>
bool canBind = false;
TSharedRef<FInternetAddr> localIp = ISocketSubsystem::Get(PLATFORM_SOCKETSUBSYSTEM)->GetLocalHostAddr(*GLog, canBind);
return (localIp->IsValid() ? localIp->ToString(false) : "");
And in file ProjectName.Build.cs:
PublicDependencyModuleNames.AddRange(new string[] { /*Some more stuff*/ "Sockets" });