I remember someone else having issues updating the firmware of a device paired securely, and they ended up using PC Controller as a secondary controller to update the firmware.
Yes, exclude, then during inclusion pick Skip security when prompted. As a rule of thumb it's best to leave all devices except for garage door stuff and locks without security. Your mesh will be much happier
I'm not saying that with complete certainty. I think I remember someone else encountering the same issue with an S2 paired device. I tagged Hubitat's lead z-wave engineer for clarification.
First, just triple-check you have the correct firmware file (i.e. not mixed up with another device etc) from Zooz -- you likely do, but crazier things have happened.
Remove that update file from the device updater app to get it back to a clean slate.
Remove the device updater app, and then re-add it. I know that sounds dumb, but that often helps shake gremlins loose.
Reload the update f/w file to the updater.
Try the update again - hopefully it goes well this time!
Is the file the correct type for Hubitat to process it? I know some companies do some weird things to apparently make it more difficult to update. Ask Zooz if they sent the correct file for a Hubitat hub.
If it's any consolation, the update is possible -- I updated mine a while back using the built-in updater.
The file that gets uploaded should be this name and file extension:
ZWave_Dry-Contact-Relay_ZEN51_ZGM130_SDK7.15.4_ZOOZ_V1.40.gbl
(I just realized I can't find the file itself, but I did have a copy of the file name)
When you start the update and select the device, it should then populate the current firmware next (but before you select the updated firmware)-- does that revision number match the firmware information on the Z51's device page itself?
Have you tried rebooting the hub before trying again? Also, some devices don't update well through repeaters. Can you try getting the device and hub very close to each other?