PXELINUX network booting an ISO file

I’m trying to boot through the network with the help of PXELINUX. I’ve installed the necessary tools using the official Syslinux documentation.

My PXELINUX configuration file (/tftpboot/pxelinux.cfg/default) contains:

default menu.c32
prompt 0
menu title SPIOT BOOT MENU
    label localboot
      menu label Boot Local Disk
      localboot 0
    label 1604Install
      menu label Manual Install Ubuntu 16.04
      kernel ubuntu/linux
      append vga=788 initrd=ubuntu/initrd.gz locale=en_GB.UTF-8 keyboard-config$
    label clone
      menu label Clone Disk
      kernel clonezilla/vmlinuz
      append initrd=clonezilla/initrd.img boot=live username=user union=overlay$
    label Winux
      menu label Install Winux
      Kernel Winux/memdisk
      append iso initrd=Winux/Winux.iso raw

The menu is displaying successfully in the network connected machine:

The local disk, Ubuntu installer, and Clonezilla menu items work. The custom ISO which I’ve created (the fourth menu item in the screenshot) is not working. I don’t get any errors – it just skips without errors and returns back to the boot menu.

Fourth menu item:

label Winux
  menu label Install Winux
  Kernel Winux/memdisk
  append iso initrd=Winux/Winux.iso raw

The necessary tools like memdisk and the directory/file architectures are all correct.

My goal is to boot a raw ISO file through the network. If there are any other possible solutions, please guide me.