Yes, I created a new VM, used the same debian ISO, installed a fresh Alby Hub after that, created a new Alby account, booted Alby Hub, connected it to the new Alby account, the connection went through, I got a succes message on the getalby account page, but within Alby Hub the same error message occurred.
Discussion
and with an ubuntu machine it works?!
First try, yep
Even with my original Alby account which I connected and disconnected to Alby Hub like ten times
Last thing I can contribute here it that I used the installation script command on Ubuntu.
$ /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/getAlby/hub/master/scripts/linux-x86_64/install.sh)"
Port was 8029 here.
On debian I typed in the three commands manually.
wget https://getalby.com/install/hub/server-linux-x86_64.tar.bz2
tar -xvjf server-linux-x86_64.tar.bz2
# run Alby Hub and done!
./bin/albyhub
Port was 8080