Thank you for providing detailed information about the issue.
Unfortunately the gateway is somewhat hard to use. There was no API with which to extend WC Marketplace with payment gateways, so I had to improvise as I went along. If it turns out that the gateway does not work, then I will take the decision to decommission it.
However, I have tested refunds multiple times, and I know that they work, at least when certain conditions are met.
In your case, it looks like you attempted to perform a refund, but it did not go through, because the price of Litecoin has changed in the mean time. The amount refunded is calculated in the store currency, but is returned in the currency the user initially paid.
Therefore, if the admin account had more Litecoin, the refund would have been executed.
As a sidenote, I do not know if the Marketplace plugin or the crypto gateway are compatible with the RMA plugin you mentioned.
Yes, please do check the information given in the other thread related to refunds. I will add this information to the homepage soon.
with regards