Keyboard Maestro 5.3.2 trial expired?

I have Keyboard Maestro 5.3.2 downloaded from https://www.stairways.com/main/download

I am using this on OSX10.6.8, There is no option to buy this version and it is the newest version that will work on my OS. Despite this I am now getting a dialog when I attempt to open it saying that my trial has expired and I need to purchase, enter a license key or quit.

Is this old version supposed to be free to use, or a trial? If it is only a trial how can it be purchased?

You can only ever buy the current version of Keyboard Maestro, however that implicitly allows you to use older versions if necessary (subject to the fact that it is a single user license on up to five Macs).

Version 6 will accept version 7 serial numbers (and this is generally true for one version behind).

For Version 5 you need to contact support after your purchase to get a complimentary version 5 license added to your account.