If you mean you send me a PO, I send you an invoice, you send a check, yes I can do that.
The full calendar download is available before paying, so that you can test it and make sure it works well for you. So if you are thinking that you want to send a PO so you can download the program right away, there is no need for that. You can download, install, run, and then send the check when your process catches up 
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Scott
CalendarScript.com