Can not issue refunds on prior refunds



we are having an issue with issuing refunds on order with prior refunds.
An example: Customer we gave a restocking fee to when we first refunded the initial order, we are now not able to refund anything else even though a $90 balance remains. We have tried using the adjustments template and no matter what we do it says “The requested refund amount for the item price is not eligible.” This makes no sense. We have tried to open a case and can not get a helpful agent. Has anyone else experienced these issues and know how to fix it?