Since Plesk version 11.5, you can no longer install the the Plesk Customer & Business Manager component via the Updates and Settings are of of Plesk.
I’m hoping this isn’t a sign that Parallels are planning on ending the life of this excellent addition to the Plesk eco-system.
To install the addon, you need to initiate it from the command line via the following:
For Unix
sh#> ./autoinstaller --select-product-id plesk --select-release-current --install-component billing
For Windows
ai.exe" --select-product-id panel --select-release-current --install-component billing
In windows the ai.exe is moved to the Plesk\admin\bin folder, making it generally end up somewhere similar to C:\Program Files (x86)\Parallels\Plesk\admin\bin\ai.exe.
If you did the default install you can therefore simply run this from the command prompt:
"C:\Program Files (x86)\Parallels\Plesk\admin\bin\ai.exe" --select-product-id panel --select-release-current --install-component billing