A NACHA file is a set of instructions that triggers a batch of ACH payments as soon as it is uploaded to a bank portal.
NACHA file format is the protocol for structuring those instructions in a way that successfully initiates the payments.
A NACHA file is a list of bank accounts and routing numbers (accompanied by the dollar amount to charge). If they have a developer (or pay for pro service), it's fairly straight forward to use our API* to run a payment for each item on their NACHA file. (* - so this is not a lower priced direct merchant, but instead needs API access.
Most leads, when they ask this question, are expecting some folder they can upload to and the processor just automatically chews through the file. Paystand does not have that.