Unfortunately, the Zendesk marketplace does not have annual payment functionality.
However, if you've got your heart set on paying annually then we have a workaround for you. You can purchase a year's (or more) worth of credit and instead of the marketplace charging your credit card every month, the charge will be deducted from your credit amount.
This means that you'll still need to keep a credit card on file with the app in Zendesk because, while a prepaid balance will always be applied to the monthly charge first, if the balance is insufficient for the charge attempted, the remainder will be charged from the credit card stored.
So what if your number of agents changes during the year? Well, this still works the same as before. Changes to the number of active agents are pro-rated on a daily basis. So, depending on your agent fluctuations throughout the year, your credit balance may last longer or shorter than the time you initially estimated.
If this is something you'd like to setup on your account, or you have more questions, simply email us at firstname.lastname@example.org