Updates - 401 and no Release file

Hi Dietmar, yes I have purchased one and the key is activated on that server. I changed the Debian Repositories to:

deb http://ftp.debian.org/debian stretch main contrib
# security updates
deb http://security.debian.org stretch/updates main contrib

and for Proxmox:
deb https://enterprise.proxmox.com/debian/pve stretch pve-enterprise
commented:
#deb http://download.proxmox.com/debian/pve stretch pve-no-subscription

and still get:

starting apt-get update
Ign:1 https://enterprise.proxmox.com/debian/pve stretch InRelease
Err:2 https://enterprise.proxmox.com/debian/pve stretch Release
401 Unauthorized
Ign:3 http://ftp.debian.org/debian stretch InRelease
Hit:4 http://ftp.debian.org/debian stretch Release
Get:5 http://security.debian.org stretch/updates InRelease [62.9 kB]
Reading package lists...
E: The repository 'https://enterprise.proxmox.com/debian/pve stretch Release' does no longer have a Release file.
TASK ERROR: command 'apt-get update' failed: exit code 100
 
Hi there,
I have downloaded download.proxmox.com/debian/proxmox-ve-release-5.x.gpg, checked sha512sum ok, apt-key add, apt-key list (key appears), and still get the same error.
 
Hi there,
I have downloaded download.proxmox.com/debian/proxmox-ve-release-5.x.gpg, checked sha512sum ok, apt-key add, apt-key list (key appears), and still get the same error.

please open a support ticket over at https://my.proxmox.com to further troubleshoot this issue (for problems related to accessing the enterprise repository, this is is also possible for community subscribers which don't have support tickets otherwise).
 
Dear Aleksandr

As Fabian wrote before I opened a support ticket over at https://my.proxmox.com.
They had been very friendly and helpful and could solve that issue.

Best regards
Alexander ;)
 
I will just leave it here:
Code:
$ apt-get update -o Debug::Acquire::https=true
and
https://askubuntu.com/questions/636...with-etc-ssl-certs-ca-certificates-crt/636979
this helped me figure out, that my issue was with permissions of /etc/ssl/, there was 750, and only with 755 apt update started working.

just to shed some light into this issue: apt runs downloads (and some other operations) as unprivileged user _apt . for accessing a repository over https, it needs to verify the certificates, which by default uses the system CA certificates.