Can I purchase a plugin outright, rather than have a subscription?

Hey. I recently purchased the WHMCS integration plugin. However, it did not state that it was subscription based, so I assumed that it was a one time fee of $9.00. However, as soon as I saw through PayPal that it was recurring, I canceled the subscription. My question is, can I just buy the plugin outright, or is a subscription going to be required? I would prefer to buy it outright, and if I can't, then I guess I'll have to find an alternative plugin.