When we try to configure the DHCP service in a security zone, DHCP is not an option in the global host-inbound-traffic.

In the security zones, the system-services DHCP is not an option in the host-inbound-traffic:

set security zones security-zone TRUST host-inbound-traffic system-services dhcp
                                                                            ^
syntax error .

The answer is simple. The system-service DHCP can be configured only inside the interfaces hierarchy inside the security-zone as shown under the following:

#set security zones security-zone TRUST interfaces ge-0/0/0.0 host-inbound-traffic system-services dhcp
#commit