Plesk license key with additional key "MagicSpam for Parallels Plesk Panel" cannot be issued.
The following error appears in Action Log (Top > Configuration Director > Logging and Errors > Action Log):
[Error-TEXT: 17:52] [ERROR]  [HSPC::SimpleActionLog::report_problem] Unknown feature: LINUXMAGIC_MAGICSPAM
The error was caused by the software issue PBAS-28603 that was fixed in OBAS 4.5.3.
To resolve the issue, please upgrade to the latest version as described in How to upgrade OBAS system to the latest available version.