Hi Ashish,
I am able to resolve my issue. Now, when a approver reject a confirmation, a notification is sent to the user who created the confirmation.
Issue is resolved by implementing the badi BBP_ALERTING for BUS2203 on the event APPROVAL_PROCESS_DOC_REJECTED.
As per the SPRO configuration Define Recipient Notifications it is not possible to send the rejection notification for a confirmation since there is no standard task available for rejection of a confirmation. Please refer the below URL for the same.
Regards,
Manoj