Cannot install on Ubuntu. libffi6 is not installable

[TOASTYxTIM]

When attempting to install OpenVPN on my Ubuntu system and I am constantly given the following:

apt update && apt -y install openvpn-as
Hit:1 http://as-repository.openvpn.net/as/debian buster InRelease
Hit:2 http://kali.download/kali kali-rolling InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
319 packages can be upgraded. Run 'apt list --upgradable' to see them.
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
openvpn-as : Depends: libffi6 (>= 3.0.4) but it is not installable
E: Unable to correct problems, you have held broken packages.

I tried running: apt install libffi6 and it says it's referred to as another package. I searched for it by running: apt-cache search libff and the list that displays only shows libffi7, not i6.

If libffi6 is a dependency, how do I install it?

[chilinux]

To install libffi6, first install Ubuntu version 18.04 LTS.

If you are running Ubuntu version 20.04 LTS, then make sure you are following the install instructions for 20.04.

If you are using a version of Ubuntu other than 18.04 or 20.04, then it is not supported.