In POS & Oracle integration , there was a need to unapply and reapply receipts which are already reconciled in Cash Management . The older SAP system, does work differently thus requirement was to achieve the same in oracle EBS.
To explore API availability to unapply and re-apply receipts which are already reconciled in cash management
Solution & Out of Box Functionlity
The receipt API's work no matter what is the receipt status. A receipt that is confirmed can be applied or unapplied just the same as one that is already reconciled in Cash Management, there is no difference.
There is no connection between the application/unapply of a receipt and reconciliation in Cash management.
So you can unreconcile and then unapply or you can unapply and then unreconcile.
A receipt application refers to invoices/credit memos etc on which the amount sent by customer is closing the transaction balances.
A receipt reconciliation/unreconcile refers to the matching between a receipt and the statement sent by bank to confirm that the money paid by customer entered in your company account.
There is no link between these two business processes. A receipt can be applied/unapplied irrespective of its situation with Cash Management statement reconciliation.
The world of receipts API
As mention , in one of the post, there are 10+ API's available to handle any scenarios of receipting process in oracle.
For transactions application and unapply
- Ar_receipt_api_pub.Apply: Applies a cash receipt to a particular installment of a debit item. The application can also be a cross currency application.
- Ar_receipt_api_pub.Unapply: Unapplies the application of a particular installment of a debit item against the specified cash receipt.
- Understanding AR Receipt, Point of sale, APIâ€™s & Intergration with Oracle Application 
- Receipt & Cash Managment