Atten: Old-Bodger
Just wanted to pass on my thanks because without reading your post I was about to return my second Echo 4th Gen because I couldn't get it to connect to my wifi, despite me having a decent level of competence using routers & wifi.
I was pretty close to throwing my Echo ball as hard as I could into a brick wall but then I came across this post of yours with the secret alexa.amazon.com URL.
After returning one Echo and failing umpteen times to get setup completed, continually being told my (correct) password was wrong, I entered the Secret URL and it worked first go. I'm still stunned. From bamboo under fingernails pain to painless.
So again, I thank you Bodger.
I'm taking a break before trying to get Zigbee to work — no doubt that's going to be less than straightforward.
Cheers, Mikey