Ability to validate subscriptions via configured proxy server appears to have broken in version 9, not having issue on any nodes still on 8.
Receiving following error:

"Error checking subscription: io: failed to lookup address information: temporary failure in name resolution (500)"

indicating it is not trying to utilize the proxy

It looks to me like Proxmox can't resolve the address. Can you resolve shop.proxmox.com?

Where did you enter the proxy server?

Code:

http_proxy: http://.*
Specify external http proxy which is used for downloads (example: http://username:password@host:port/)

What's the host DNS configuration?
Please provide the output of cat /etc/resolv.conf

DNS will not be able to resolve external addresses as it is in a segmented environment. 30 + other pve hosts running on pve8 and configured same way and work fine, DNS resolution is not necessary as the proxy server handles it.

Proxy server is configured under Options tab on data center.

I tested this. A pure Apt proxy works. If your DNS resolution isn't working, you can also make an entry in /etc/hosts as an additional workaround.

I configured the proxy for Apt like this: /etc/apt/apt.conf.d/01proxy

Code:

Acquire::http { Proxy "http://myProxy:3128"; };

The proxy you configure in Proxmox Datacenter is usually entered in this file:

Code:

/etc/apt/apt.conf.d/76pveproxy

But unfortunately, that didn't work in my tests.

Making an entry in hosts would not direct the traffic through the proxy though? Internet is only accessible through the proxy.

I was able to trick it into working by putting in a dummy record in host file for shop.proxmox.com does not need to be the actual IP just something for it to get an Ipv4 address it appears. subscription check succeed afterwards.

broken here too, any idea when this will be fixed?

I was able to trick it into working by putting in a dummy record in host file for shop.proxmox.com does not need to be the actual IP just something for it to get an Ipv4 address it appears. subscription check succeed afterwards.

I used the same workaround and can confirm that a dummy ipv4 record on each host allows the license to validate. Thanks for the info.

I was able to trick it into working by putting in a dummy record in host file for shop.proxmox.com does not need to be the actual IP just something for it to get an Ipv4 address it appears. subscription check succeed afterwards.

Thanks for this, it worked for me on 9 PVE nodes.