New "feature" - "ThinOS customer activation license"

I would advise you to have a conversation with your Dell sales team who can explain it. 

Not that it helps much, still about as clear as mud, but there's more information in the actual release notes for ThinOS 2205: https://www.dell.com/support/manuals/en-us/wyse-5070-thin-client/thinos_9_3_x_rn/thinos-enhancements

Found more information here, apparently it requires WMS 3.7: Dell Wyse Management Suite Version 3.x Release Notes | Dell US

Here is what happened with mine:

I bought mine through Newegg Business, and the seller claimed to be selling a NIB unit. I got it, installed it, and configured it, and all worked well until last week when I attempted to upgrade the unit to ThinOS 2205, when I got this same error message. I went through forums and read through the release notes, checked the bottom of my unit and didn't see a PCOIP sticker. I decided to try manual upgrades via USB, and when I got to the boot options, I saw an option for Ubuntu. I didn't think anything of it at first, but after a failed manual upgrade (error 233) and some further investigation, I figured out that this unit did not originally have ThinOS installed; it had ThinLinux and was flashed with ThinOS at some point. This aligns with the scenario below, which means I'm either stuck with ThinOS 9.1, or I need to obtain an activation license.

• Devices that are converted from other operating systems must use the ThinOS activation licenses to enable VDI function. Without the ThinOS activation license, you cannot log in to any Broker agent on the devices. The ThinOS activation licenses are used automatically when registering to Wyse Management Suite.

Bottom line: If you think your device shouldn't require an activation license, check the boot options to be sure it doesn't also have Ubuntu listed as one of the options. Hope this helps someone else running into this same problem!