I struggled a bit (see my other post here) and rooted the tablet, but now it functions. It was well worth it. What a pleasure to go to the app store and everything is free! My kid got all the games and she loves the planetarium.

SOLVED!

Typing in that order 3 lines of code :
adb devices
adb reboot bootloader
fastboot flashing unlock

Finally did the trick!

UBP took over and installed Ubuntu Touch!