first, thanks for the screenshot - it explains things really well.
we have been having a normal rate of installs in recent days, so the repos are up and running, they appear ok and the logs look ok, so it's all good from this side.
the url is correct from your side.
is it possible that you don't have proper networking at that stage?
you can press ctrl-alt-f2 and there should be a shell there. you can try
and also for reference
there could also be glitches in the repo side or the path from you to the repo, so trying again a bit later may help (though i assume you have done that already).