The submitted (monthly) claims and unclaimed amount will be accounted at the year end for tax calculation. By default the application is configured to consider the unclaimed amount at the end of the year for payment.
This option is set in the Preference section. If this option (button) remains checked, the unclaimed amount for the current month get calculated while processing thereby restricting the employees from applying for that month's claim.
See the illustration below to uncheck the option before payroll process.
Once the claims are submitted this option has to be checked before payroll process to consider the unclaimed / differential amount for tax calculation