Is this just not doable at all?

Dave

You can do preliminary validation if you can find the validation
formula -- it's not exactly secret, but you do have to make an
application to a bank, and promise that the code will not be
released.  So you may not easily find a VBA sample solution
for preliminary validation.

Or find it on a warz site.  (Although anything you find on a
warz site is more likely to be full validation rather than preliminary
validation)

Full validation is supposed to be secret, you won't get that
because it allows you to generate valid credit card numbers.
Preliminary validation helps you prevent transcription errors.

Most of the bank bach interfaces are not really sophisticated.
You really need to talk to your bank - it will probably just be
a comma separated file with one line per transaction.

The banks do talk from time to time about standardisation,
but only when their private technology is so out of date as
to be unusable -- once they get going again they diverge again,
and they never turn off old systems,  they just add new systems
as required, which is not very often.  There are hundreds of
bank transfer protocols - and at least one company making
a living from bank protocol translation software.

(david)