I've been trying to setup this Eero 6 off & on for 2 days now.
I did buy the unit 2nd-hand from a fellow on Facebook Marketplace. It was 1 of 4 devices i purchased, the other 3 were different manufacturer/model & those work great.
This Eero 6 unit was by itself.
I followed the in App(for Android Samsung Galaxy A70 - Android Version 11) instructions which failed with the same error several times. After multi attempts i came to the internet looking for answers. . .
Found a previous post here in the Community (Eero fail registration) and saw this suggestion posted by eero support person[michael_eero_support]
"For this error message try unplugging both the modem and the eero from power for at least three minutes, plug the modem in first, wait for it to boot, then plug in the eero.  Wait for the eero to get to the blue led (flashing or steady), give it a minute and try again."
So i tried this a few more times, i would even go into my mobile phone and clear the cache for the eero app in between attempts thinking that could also be a possible issue, all to no success - constant error "We Found an Issue"
I also inter-mixed soft(yellow-7 second) and hard(red-15 second) resets
The fact that i bought it 2nd-hand, could it still be registered to a previous owner?( is that a thing? ) Could it be part of a pair and not be used individually? Could the previous owner have changed a setting that doesn't reset when you Soft or Hard Reset the device?
I've included a screen shot of the label on the bottom of the device . . .
Thanks in advance regardless of the answers i get back, it's good to see a place where you can at least ask the questions.

Kevin