If you offer Seller Pays for postage the old ' Free Postage' method, you will still be given the Simple Delivery label if you are then selecting to use you own delivery / postage service.
Here then, you'll need to manually cancel the label and do this within 14 days for a refund of that unused label.
You'll need to fill out the Request a refund for Simple Delivery form for the label that wasn’t used.
@ianhonda4you