Guys and girls this is my solution that worked today.
I too have had this problem for 3 days since getting a new firestick 4K.
my advice that worked for me
reset to factory settings
automatically let it update after signing into amazon account.
there are at least 3 updates
the latest ones are :
software version fire os 6.2.7.6 (NS6276/2933)
fire tv home version 6242054.1
once updates start take the firestick out the HDMI but leave it plugged in, wait at least 3 hours and check if updates are all as they should be above. (The home version is the final update and not obvious)
if they aren’t then restart and again take it out the HDMI and wait again.
i had the same error verification failed, it has nothing to do with 2 way authentication As it wouldn’t even let me sign in or create a new account
try downloading Apple TV and see if this works.
if it doesn’t..... Then further restart and leave overnight for 8 hours, again plugged in to power ...
this morning it finally worked after getting it Sunday. (It’s now Tuesdays) and QR code came up and no more verification failed error.
its a ball ache to wait but the above method does work.
LT