A paper bank reconciliation has two sides. Start the bank side with the statement balance, add deposits in transit and subtract outstanding checks. Correct a bank error on that side until the bank fixes it. Start the book side with the ledger cash balance, add unrecorded bank credits and subtract fees, NSF items and other unrecorded charges.
The adjusted balances must agree. Timing differences usually require no journal entry because they are already in the books. Book omissions do require entries. An NSF customer check restores the receivable and reduces cash; it does not reverse earned revenue automatically. Read whose records contain the error before deciding which side needs adjustment.