Is it possible to change the number of IP addresses in the Plesk Client Hosting Plan to zero?
In Odin Business Automation Standard (OBAS) versions prior to 4.5.6 dedicated IP addresses assigned to Plesk client were a non-downgradable resource and could not be downgraded directly from the control panel.
The following error was shown upon attempt to downgrade the resource through Control Panel > Account > Buy Resources:
Number of IP addresses cannot be lower than N ip(s)
Such behavior was classified as the software issue #PBAS-18775 and was fixed in OBAS 4.5.6 release.
To resolve the issue, please upgrade to OBAS 4.5.6 version as described in How to upgrade OBAS system to the latest available version.