Nick, I'm not sure if I'm barking up the right tree or not, but it sounds like you are charging a NSF fee for the loan payment. You need to look at your state law. In IN we can charge (if contracted for) a $20 NSF fee for loan payments presented that are NSFs. If we are also the depository bank, we can charge the $20 loan NSF fee and our deposit NSF fee which is currently $25.
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The opinions expressed are mine and they are not to be taken as legal advice.