You should understand on which interfaces you can configure DHCP services for each deployment mode.
Bridge Mode: The MGMT interface is the only interface that can be configured as a DHCP server.
Software Switch: By default all interfaces except the MGMT interface are L2 interfaces that are part of the software switch. The WAN, LAN1, and LAN2 interfaces must be included in the switch configuration.
You can, if desired, remove LAN3 from the switch configuration. After you remove the LAN3 interface from the software switch configuration, you can change it to an L3 interface, assign it an IPv4 address, and then enable DHCP services on the interface.
Bridge Mode: The MGMT interface in the only interface that can be configured as a DHCP server.
All interfaces except the MGMT interface are L2 interfaces and are part of the switch configuration. They cannot be removed from the switch configuration and cannot be configured as DHCP servers.
Bridge Mode: Only the MGMT interface can be configured as a DHCP server.
Routing Mode: All L3 interfaces can be configured as DHCP servers including the main and guest wireless network interfaces.
DHCP services are enabled by default on a wireless network interface. By default, when you enable a wireless network, DHCP services will be enabled on the interface.
However, if DHCP services on a wireless interface is disabled before enabling the wireless network and the wireless network is later enabled, the DHCP services will not be enabled when you enable the wireless network. In this case, you must manually enable the DHCP service on that wireless interface.