Backup of Proxmox fails

Hello,

I have a problem with Proxmox Backups. I have only my Home Assistant running on Proxmox and I want to backup it to a Qnap Nas.
The Nas Folder is added successfully but when I try to backup on this path, Proxmox gives the following error:

INFO: starting new backup job: vzdump 100 --mode snapshot --remove 0 --notes-template '{{guestname}}' --notification-mode auto --compress zstd --node pve --storage Backups_Proxmox
INFO: Starting Backup of VM 100 (qemu)
INFO: Backup started at...

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