Return Label Cost (FBM)

Hi guys, for returns I purchase a label from Royal Mail online and send it to the customer. I do this for most returns, because often trying to have the customer pay for a label causes issues, so I take it on the chin and just cough up for a label each time.

When I add the label in the return there’s a box for return label cost - I always fill this out, but does it do anything? It’s also displayed on the returns screen.

Where does that money go? Is it refunded if the buyer chose a change of mind option for the return? Am I charged it by Amazon again even after buying postage from the Royal Mail site? Can’t seem to figure out if it does anything or if there’s some kind of payment or reimbursement associated with it. (Wishful thinking eh?)

Thanks.