Unable to download or access huge backup file (more than 20 GB or with multiple incremental backups) in Tools & Settings > Backup Manager > Backup > Download, one of the following errors is shown:
504 Gateway Time-out
This operation is taking too long. Check the results in a few minutes.
Insufficient timeout limits set for Plesk.
Connect to the server via SSH
/etc/sw-cp-server/configfile using a text editor
Adjust timeout limits for FastCGI to the following:
/usr/local/psa/admin/conf/php.inifile using a text editor
Adjust timeout limits for PHP:
max_execution_time = 1200
# service sw-engine restart
# service sw-cp-server restart
If the issue still persists increase timeout limits even greater.
Alternatively, it is possible to download the backup directly from the server via CLI bypassing Plesk interface.