Help with VLAN

Hello guys,

I'm not a networking expert at all as i've started playing around with Ubiquiti UniFi switches and AP just recently with no experience before that.

I'm a bit confused right as to why my setup isn't working, so i'll try my best to explain the situation:

We have a bunch of access points with 2 SSID, one for users and one for guest users (which includes employers' phones and tablets) and i've set them up initially to share our production network with some guest policy set up in the Unifi Controller.

Now i've got a problem, our DHCP server, which runs on a machine with Windows server 2008 R2 (I know, it's old af but an upgrade is on its way), is nearly full as the number of guest users has increased lately.

So I thought it would be better to create a VLAN for guest users only.

I've got a Stormshield SN300 firewall in which i've configured a VLAN on the internal interface with ID 100 and assigned a static IP (192.168.100.201/24) on the firewall for that VLAN.

I've set up a VLAN only network in Unifi Controller (with ID 100) and enabled the "use VLAN" flag in the Wi-Fi network settings of the Guest network.

Last step was to create a new scope in the DHCP management of the Windows server and enable DHCP relay on the stormshield firewall.

As i've done all of this i've tried connecting to the guest network only to find out the laptop i was using could not reach the DHCP server. I have even tried to set up a static IP address on the WLAN interface of the laptop but i can't ping either the firewall nor the DHCP server.

So i'm stuck for now. I admit that i have only read about VLANs and never actually used them so most probably there's a problem in my setup.

Thank you very much for your help.