wordpress-toolkit error during backup

Hi everyone, I am struggling for some days now, when I try to run the backup of a specific WP installation I get this error:

Errore nel backup del sito

• Failed to copy file /var/www/vhosts/vps1.ewhost/domains/domain_name.com/wp-content/. to /var/www/vhosts/vps1.ewhost/.wp-toolkit/backups/24/files/wp-content

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What should be the issue related to? I have made backups of other websites through Wordpress-toolkit and the succeeded with no issues.

Thank you