403 from au.archive.ubuntu.com

Solution 1:

Easy fix

Switch to the main archive or use a different mirror. Mirrors can be found at https://launchpad.net/ubuntu/+archivemirrors

Slow fix

One option is raising a ticket with aarnet about the issue and they'll fix it, I've done it many times with iinet, but tickets usually take time, and the issues usually resolve themselves before action for many packages anyway (ie. new update arrives & users don't want that package any more)..

Tickets have been raised

I've spoken (typed?) with users experiencing the same issue on IRC (#ubuntu), and one has reported they'll file a ticket (bug reports) with aarnet.

I've since switched to another focal box myself that was using mirror.aarnet.edu.au & experienced the same error; thus I've emailed the "AARNET Mirror Team" about the issue, so it's been ticketed, so the fix should occur in due course.