Hourly error in Plesk panel.log: Protocol version '1.6.3.0' is deprecated. Current protocol version is '1.6.9.1'.

Symptoms

• Plesk Obsidian running on a Linux-based operating system
• WHMCS is connected to the Plesk server
• During every hour, the /var/log/plesk/panel.log receives a warning that is similar to the following:
  

  CONFIG_TEXT: Protocol version '1.6.3.0' is deprecated. Current protocol version is '1.6.9.1'.

Cause

One of the Plesk domains on the server contains a WHMCS application installed which is sending warnings during the execution of its cron task. The cron task that is being executed is similar ot the following:

# /opt/plesk/php/8.1/bin/php -q /var/www/vhosts/example.com/crons/cron.php do --ServerUsageCount -vv

Resolution

Such warning messages do not affect functionality of Plesk or WHMCS and can be safely ignored.

The messages are caused by the external API of WHMCS, which is trying to reach Plesk using an old and deprecated version of the XML API protocol.

The warnings in question can be resolved permanently only on the side of WHMCS, as it is related to the code of WHMCS application files. If you wish, you may contact WHMCS support in order to report the issue to their technical support team by following this link:

Technical Support | WHMCS