> submit a transaction via an online API as a debit rather than credit

Yes, via ACH/SEPA Direct Debit but I don't believe it's common outside of Europe.

Processors, like First Data, will know at the point of transaction if it's a credit card, debit card, or even a prepaid card. Though it's been a few years, I remember the Adyen API returning all of this in the pre-auth response (had a business that didn't accept payments from prepaid cards, fraud was too high).

It's also possible this is encoded in the BIN/IIN (1st 6 digits), but my memory is fuzzy on the specifics.

BIN will tell you if its prepaid/card type. There's some weird rules around prepaid, like your can't set the recurring flag on prepaid on non-reloadable cards.

Adyen says they can route cards on different networks though i never used them personally.

It seems to be attached to the BIN. Our processor has a bin endpoint where I feed it the first 6 and it returns a bunch of info about the card, including credit/debit.