Purge invalid transactions in cash management

Hello,

The business created external transactions in May - Jun but they didn't run the create accounting process, they'd close those period and didn't notice the warning on the exception report and the transactions are as "invalid". In Aug they have accounted the amount with a manual journal.

My question is: if they can purge the transactions? whay implications have this purge? is there any other option?

Thanks

Regards