If your version was 5.xx that means you have use old version. For V5 does not need licence key. You can find that in download section - old firmware
If you have already activated v4.16 you can upgrade to v4.2 without worries.
You have make upgrade from free V5 to V4. In that case need licence key.

I just updated the firmware on my ATS25X1 and my license key for the existing firmware didnt transfer. Does this mean I have to purchase another license or do is the license recoverable against the hardware?

Thank You, Any time when need help.
73's

I purchased an activation key from Ats Key<atsxkey@gmail.com>
And it worked fine and they were very helpful with the setting up process as I was making a mistake with it. Happy to recommend ,super service.