What prevents errors from happening when the bar code is read? As an example, can a transaction that is supposed to be $40. be read by the machine as $400. I just want to know if errors ever take place when the bar code is read and what safeguards are in place to prevent that.

We use encryption to verify the barcode data being sent from the ATM and check it against the EZcash database. Any unauthorized barcodes (such as one on a box) would be kicked back is invalid.