BPA workflow error : class java.lang.Integer cannot be cast to class java.math.BigDecimal (java.lang.Integer and java.math.BigDecimal are in module java.base of loader 'bootstrap')

I am trying to set Voucher Status automatically using a Workflow   and getting above error for the below method.

 - VoucherEntry_ReadyToUpdate():Void

Here I am triggering an Event when a Voucher get status “Approved”.

And the workflow is trying to set the status as “Approved” of the  Vouchers with the same no and awaiting approval in other companies.

Before calling method VoucherEntry_ReadyToUpdate  , workflow reads the Voucher  

Same Error appears  for  hardcoded vales.

Any advice how to avoid that Error is highly appreciated.  Thanks in advance for your help!