Yep, others are having the same issue today, many reports of this coming through, you are not alone. It's a technical issue as with all of these annoying glitches, it can be just a case of ..... ' please try again later'.
Or, for the time being, the answer is to either buy your own postage label through Royal Mail / Post Office, or as said, try again a little later on, for an SD label.
Then, for the unused label:
- If you selected 'Buyer pays’ when you created the listing, your buyer will automatically be refunded for any Simple Delivery label that isn’t used after 30 days
- If you selected ‘Seller pays’ and offered free postage on your listing, you'll need to fill out the Request a refund for Simple Delivery form for the label that wasn’t used. Make sure to send your request within 14 days of your item selling.
@dapeng-13
@hubsteruk