DHCP not being set on edge gateway - what's different to a firewall being set?

I have an edge gateway that I can set firewall rules on, and nat however when I try to add DHCP through powercli I don't get an error but nothing get's applied to the gateway, can anyone help?

Here is the function I have:

function configureDHCP {

        param ([String]$gwName )

        $edgeGWview = Search-Cloud -QueryType EdgeGateway -name $gwName | Get-CIView

        $dhcpService = New-Object vmware.vimautomation.cloud.views.dhcpservice

        $dhcpService.DefaultLeaseTime = "3600"

        $dhcpService.MaxLeaseTime = "7200"

        $dhcpService.IsEnabled = $true

        $dhcpService.IpRange = New-Object vmware.vimautomation.cloud.views.iprange

        $dhcpService.IpRange.StartAddress = "192.168.1.1"

        $dhcpService.IpRange.EndAddress = "192.168.1.254"

        $edgeGWview.ConfigureServices($dhcpService)

}

Interested to understand why DHCP is different and what I'm doing wrong. The API guide here does'nt really help as page 187 just says do the same thing as before (eg Firewall rules).

This has been a great source so far but doesn't cover DHCP.