After installing Proxmox Backup Server (PBS), the system is configured to use the Enterprise Repository by default.
This repository requires a paid subscription, and without one, you may see errors such as:

401 Unauthorized
You do not have a valid subscription

Fortunately, Proxmox provides a No-Subscription (Community) repository, which allows free access to updates and security patches.
This guide documents the complete process for converting PBS 4.x (Debian 13 trixie) to the community update channel.

✅ 1. Verify Your System Version

PBS 4.x is based on Debian 13 (trixie).
Check your system version:

cat /etc/debian_version

If you see 13.x or trixie, your system matches PBS 4.x.

✅ 2. Disable the Enterprise Repository

The default enterprise repository is located at:

/etc/apt/sources.list.d/pbs-enterprise.sources

Edit it:

nano /etc/apt/sources.list.d/pbs-enterprise.sources

Comment out the entire file or set:

Enabled: no

Example (fully disabled):

#Types: deb
#URIs: https://enterprise.proxmox.com/debian/pbs
#Suites: trixie
#Components: pbs-enterprise
#Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
#Enabled: no

This completely disables the enterprise repo.

✅ 3. Add the Community (No-Subscription) Repository

PBS 4.x uses the modern Deb822 format (.sources) for APT repositories.

Create the file:

nano /etc/apt/sources.list.d/proxmox.sources

Insert:

Types: deb
URIs: http://download.proxmox.com/debian/pbs
Suites: trixie
Components: pbs-no-subscription
Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg

Important details:

Field	Description
URIs	Official Proxmox PBS repository
Suites	`trixie` (required for PBS 4.x)
Components	`pbs-no-subscription` = Community repo
Signed-By	Uses the unified `proxmox-archive-keyring.gpg`

✅ 4. Install or Fix the Proxmox Keyring

PBS 4 uses a new APT signing key:

/usr/share/keyrings/proxmox-archive-keyring.gpg

If the file is missing, download it:

wget https://download.proxmox.com/debian/proxmox-archive-keyring.gpg \
     -O /usr/share/keyrings/proxmox-archive-keyring.gpg

chmod 644 /usr/share/keyrings/proxmox-archive-keyring.gpg

This ensures APT can verify Proxmox packages correctly.

❌ 5. Remove Old Bookworm Repositories (Important)

If your PBS has been upgraded or manually configured before, you may still have a leftover:

Suites: bookworm

This will break updates because PBS 4.x must point to trixie.

Remove outdated repo files:

rm -f /etc/apt/sources.list.d/pbs-no-subscription.sources
rm -f /etc/apt/sources.list.d/pbs.list
rm -f /etc/apt/sources.list.d/proxmox-backup-server.list

Only one repository file should remain for PBS:

/etc/apt/sources.list.d/proxmox.sources

✅ 6. Update the System

Now refresh the package lists:

apt update

You should see:

http://download.proxmox.com/debian/pbs trixie pbs-no-subscription

And no more:

401 Unauthorized
“repository is not signed”
“Missing key …”
references to bookworm

Finally apply updates:

apt full-upgrade -y

🎉 Done! Your PBS Is Now Fully Using the No-Subscription Repository

After switching, you’ll enjoy:

Free access to PBS updates and patches
No enterprise subscription errors
Full functionality with all Proxmox features
Clean and secure repository configuration

Your PBS 4.x system is now running the correct community-supported update channel.