Refunding the return postage and packing .

Description

I have agreed to accept a return from my buyer and to refund them the price they paid including postage and packing and I have also agreed to refund the postage costs for their returning the item to me. I have tried to add their costs for return to the refund but this does not work. It seems that it will only allow me to send the amount the buyer originally paid. Can anyone advise how I can increase the Paypal payment I send. Thanks