The difference between annual and monthly billing in Clustdoc is the frequency at which the provided billing information will be charged with a Clustdoc invoice.
Monthly Billing Plans: renew every month and can be cancelled anytime (for example, you can use it for only 1 month and then cancel). After cancelling the renewal, you will not be charged again and can use any remaining requests until the end of your billing period.
Yearly Billing Plans: a single billing at the beginning of the plan for the next 12 months. It renews after the first 12 months.
Yearly Plans with monthly instalments: (If applicable) a 12-month engagement with the ability to pay monthly. The annual amount will still be due.