When you sign up for a paid plan for the first time, you will have to make a pre-defined advance payment based on the plan chosen and the number of employees and your account will be charged with the amount of your first payment. Subsequently, each month, an amount would be deducted from your account balance based on your usage (the formula for usage calculation is mentioned in the next answer) and you can continue using the application as long as you have sufficient balance in your account.
When you run out of balance, you will need to recharge your account by selecting a recharge option and making an online payment for the recharge amount. You can view a complete history of your account balance, usage, and payments under ‘Account Balance’ in the ‘Payroll Settings’ tab.