The deep packet inspection module is closely linked to the kernel. Artica's teams are in charge of producing packages according to the Linux kernel you have.
If the module is not correctly installed for your kernel, you won't be able to install the feature
On the left-menu, go to Your system > Update > Packages center
On the search field, type firewall
Click on the install or Upgrade button under the Firewall addons row
the screen displays a list of available modules, allowing you to choose the one that corresponds to your kernel (others will be grayed out and prevented from updating).