Imunify360 license can't be registered on a Plesk server: "License is invalid for current server"

Symptoms

• An Imunify360 license is reported as invalid upon attempting to register it on a Plesk server:

  CONFIG_TEXT: [2025-02-06 13:36:10] [2025-02-06 13:36:10] Checking if has already been registered... 
  [2025-02-06 13:36:29] WARNING: License is invalid for current server 
  [2025-02-06 13:36:29] [2025-02-06 13:36:29] WARNING: License is invalid for current server 
  [2025-02-06 13:36:29] Register by key... 
  [2025-02-06 13:36:29] [2025-02-06 13:36:29] Register by key... 
  [2025-02-06 13:36:32] WARNING: License is invalid for this server 
  [2025-02-06 13:36:32] [2025-02-06 13:36:32] WARNING: License is invalid for this server 
  [2025-02-06 13:36:32] Registration was not successful. Exiting. 
  [2025-02-06 13:36:32] [2025-02-06 13:36:32] Registration was not successful. Exiting.

• The license status is invalid upon checking with the Imunify CLI tool:

  # imunify360-agent rstatus
  WARNING: License is invalid for current server
  #

Cause

There are more users hosted on the server than allowed by the license limit.

Resolution

1. Check the user amount needed for the license:

   How to choose Imunify360 plan?

2. Upgrade the license to cover all users:

   How to upgrade user amount for Imunify360 extension?

Additional information

• What does "user" mean when buying a license? Types of licenses | Imunify Security Products — CloudLinux Knowledge Base
• License is invalid for this server. How to count the number of existing users on the server? | Imunify Security Products — CloudLinux Knowledge Base