I have a similar question. If we receive an r10 for an alleged unauthorized transaction but haven't received the documentation, even though we have requested it, can we reject the r10?
there is no dishonored return reason code for rejecting a R-10, so no, it goes outside of ACH to resolve
(and you've posted this question in multiple places, moving forward you would be better served starting a new topic with this one question instead of trying to tag multiple places for it to be seen - as a new topic is has its own visibility, just a suggestion)