Thank you for posting question @Jack45
There is no specific license to enable HA, however both firewalls should be running identical set of licenses (For example both Firewalls running TP, WF,... licenses). Here is a link for HA pre-requisites:
All what you have to do is to proceed with HA configuration on both of PA-220: https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-web-interface-help/device/device-high-availabili...
PA-220 does not have any dedicated HA ports, so you will have to use regular data plane ports. The rest is the same as documentation. If you get stuck with your HA configuration do not hesitate to post your issue here.
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