How to fix W: Failed to fetch URL 403 Forbidden in APT

First, determine which repositories are causing the 403 error:

sudo apt update 2>&1 | grep -i "failed\|403"

This will show you the specific repository URLs that are returning 403 errors.

View all currently enabled repository sources to identify problematic ones:

grep -r --include='*.list' '^deb ' /etc/apt/sources.list /etc/apt/sources.list.d/

Note any PPAs or third-party repositories that appear suspicious or unfamiliar.

Remove or disable the failing repositories. For PPAs, you have several options:

Option A: Via GUI (Ubuntu/Linux Mint)
1. Open Software Sources from the system menu
2. Find the problematic repository in the PPAs or Additional Repositories tab
3. Uncheck it to disable it
4. Click Close

Option B: Via command line
Find and remove the problematic .list file:

sudo rm /etc/apt/sources.list.d/repository-name.list
sudo rm /etc/apt/sources.list.d/repository-name.list.save

For example, if jonathonf-python-3.6-ubuntu.list is failing:

sudo rm /etc/apt/sources.list.d/jonathonf-python-3.6-ubuntu.list*

If the repository URLs use HTTP, try switching to HTTPS for better compatibility:

sudo sed -i 's|http://archive.ubuntu.com|https://archive.ubuntu.com|g' /etc/apt/sources.list
sudo sed -i 's|http://security.ubuntu.com|https://security.ubuntu.com|g' /etc/apt/sources.list

Then try updating again:

sudo apt update

If the default repository is still inaccessible, switch to an alternative mirror:

On Ubuntu:
1. Open Software Sources
2. In the Ubuntu Software tab, change the Download from dropdown to a different server (e.g., a regional mirror)
3. Click Close and try updating again

On Debian:
Switch to deb.debian.org which provides reliable access:

sudo sed -i 's|http://deb.debian.org|https://deb.debian.org|g' /etc/apt/sources.list

If you're on Linux Mint, try the maintenance cleanup:

1. Open Software Sources from the system menu
2. Click the Maintenance tab at the bottom
3. Click "Purge residual configuration"
4. Close Software Sources
5. Try updating again:

sudo apt update

If the issue persists, verify network connectivity:

# Test DNS resolution
nslookup archive.ubuntu.com

# Test HTTP connectivity to a repository
curl -I http://archive.ubuntu.com/ubuntu/dists/

# Check for IPv6 issues
ping6 archive.ubuntu.com

If IPv6 connectivity is causing problems, you can disable IPv6:

Via Network Settings GUI:
1. Open Network Connections
2. Edit your connection
3. Go to IPv6 tab
4. Set dropdown to "Ignore"
5. Save and restart the network connection

Via command line (temporary):

sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1

After making changes, verify that apt update works correctly:

sudo apt update
sudo apt upgrade -y

If all repositories are now accessible, you should see success messages for each repository source.