The keygen utility is used to generate the subscription keys and email them off to the subscriber.  Normally it will be invoked automatically on the receipt of the payment for a subscription.  However, it can also be run manually. If you run it manually you can run it in either GUI or command line mode - but for the GUI mode you need to have an environment that supports this, ie a Windows or unix desktop system.

See here for its installation instructions.

Invoking keygen with the --help option will display the following:

To run in GUI mode, start with no arguments
To run in Command Line mode, provide arguments
If you cannot run the program in GUI mode, then you must use the --server option
 to set the mail host's parameters. These are saved in the keygen.properties
 file in the .openvpms directory in the current user's home directory.
 This file can be edited if you need to change the template data.

Command Line Usage: java org.openvpms.subscription.keygen.KeyGenerator
                (-o|--organisation) <organisation> (-s|--subscriber) <subscriber> (-e|--email) <email> [(-d|--date) <date>] [(-i|--iSubDate) <iSubDate>] [-v|--verbose] [--validateOnly] [-?|--help] [--server serverParam1,serverParam2,...,serverParamN ] [--bcc <bcc>]

  (-o|--organisation) <organisation>
        Organisation Name - eg -o "Bloggs Vet Services Inc"

  (-s|--subscriber) <subscriber>
        Subscriber Name - eg -s "Dr Joe Bloggs"

  (-e|--email) <email>
        Subscriber's email address

  [(-d|--date) <date>]
        Date subscription expires in dd/mm/yyyy format - default Today+1year
        Must be after today's date if specified (default: 07/11/2015)

  [(-i|--iSubDate) <iSubDate>]
        Initial subscription date in dd/mm/yyyy format
        - if specified, is used to calculate the expiry date

  [-v|--verbose]
        Displays verbose info to the console

  [--validateOnly]
        Only validate - no subscription will be emailed

  [-?|--help]
        Provides usage documentation

  [--server serverParam1,serverParam2,...,serverParamN ]
        Set the mail server parameters name, port, user, password - eg
        --server mail.bigpond.com,25,tg[at]bigpond[dot]com,tg1234

  [--bcc <bcc>]
        Set the bcc address - to clear use --bcc #
        
        If --server or -bcc are used, other options (except verbose) are ignored