SA 85251 – Adding deletion reason in audit trail when navigating to Transactions > Financial > View Audit Trail, is not yet possible in NetSuite and it is currently an logged as an enhancement.
Alternatively, users may view the deletion reason by following below steps:
-Navigate to Transactions > Management > Transaction Numbering Audit Log
-User can customize the page by clicking “Customize View” and filter it by transaction record
-Change the search title
I went ahead and edited my response to have the full SA article, oversight by me originally to not put the whole solution in.