Possible causes:

• The plugin folder name is incorrect

• The plugin is not placed in the correct directory

• Redmine was not restarted

How to fix it:

• Ensure the folder name is exactly:
  brt_customizer

• Verify the path is:
  /redmine/plugins/brt_customizer

• Restart Redmine and reload the page

• Check log/production.log for startup errors