If a case assignee is unable to process or reconcile a payment instruction due to incorrect or insufficient information such as invalid account number, the account is closed, name and account do not match, etc., it returns UnableToApply (camt.026) message to the case assigner. If the case assigner cannot perform corrective action on the original payment instruction, it should return it to the previous party in the payment chain. 
If the case assigner returns the UnableToApply message to the previous agent, it sends a NotificationOfCaseAssignment to the case assignee.  The case assignee that will perform the corrective action sends a NotificationOfCaseAssignment (MINE) message to the case assigner and it is forwarded to the party that initiated UnableToApply.

After performing corrective action, the case assignee returns the ResolutionOfInvestigation message with status code CWFW – cancellation will follow or MWFW – modification will follow which is routed to the agent that sent the UnableToApply message.  

The case assignee then sends a CustomerPaymentCancellationRequest (camt.055)  or FIToFIPaymentCancellationRequest (camt.056) or RequestToModifyPayment (camt.087). 
If the case is reopened i.e. cancellation or modification follows UnableToApply, then the case identification of the UnableToApply message is used in the cancellation or modification messages to follow up the original workflow with the CaseReopenIndicator flag set to true.

Illustration - Payment is Not Paid as Instructed or Details are Invalid

If the Creditor Agent is unable to process the Customer Credit Transfer request, it returns the UnableToApply message to the previous party in the payment chain.

The initial CustomerCreditTransferInitiation message sent from Debtor to First Agent, CustomerPaymentStatusReport, and BankToCustomerDebitNotification messages sent from First Agent to Debtor is not included in this diagram.