@Trep76470 A windows dhcp server should work just fine. Is it OK to guess that your fog server is at ip address 192.168.21.220?
The error message you first posted usually indicate a bios computer booting, but I don’t know leovo computers pxe boot process. Typically uefi computers would mention NBF.
Are the pxe booting computers, dhcp server, and FOG server on the same IP subnet? If yes then we can use tcpdump running on the FOG server to capture what is actually flowing down the wire.
Some things to check on your dhcp server.
Make sure it is responding to both dhcp and bootp requests. Both bits of information need to be in the dhcp OFFER packet. If you have redundant dhcp servers, make sure you configure dhcp options 66 and 67 on both servers. Microsoft’s HA for dhcp does not copy over these settings.If you can not find the solution then I have a tutorial here: https://forums.fogproject.org/topic/9673/when-dhcp-pxe-booting-process-goes-bad-and-you-have-no-clue
Look at the results with wireshark, specifically the OFFER packet. Look to see what dhcp servers are responding to the offer packet. Then in the offer packet look at the ethernet header. You are interested in the next-server and boot-file fields. They need to be populated and match the dhcp options 66 and 67 under the dhcp options section. If you can not understand what you see in the pcap file, then upload it to a file share site and then either post the link here or DM me using fog chat the url and I will look at it.