NSF with EFT and/or ACH Transactions
Debit card is technically a EFT. But so is ACH. EFT is electronic funds transfer so its pretty open ended. Debit card will tell you NSF, but ACH takes 3 days to tell and will approve immediately but come back later with NSF.
Debit Card -- should be instant rejection of NSF. However, some banks will still honor a slight overdraft and complete the transactions. ACH will go through no matter what, and then your virtual terminal has something called Reject Reports. We don't get notified when they happen so we cant show it in our system.
For us on Sage, we get emails for "Reject Reports" every week or two. This is a setting you can enable at a gateway level.