When did you earn those eBay Bucks?
eBay Bucks certificates are issued quarterly and are good for a whole year, so any Bucks earned this quarter will not be issued until January 3rd or so. The Bucks you can spend right now should appear at checkout as a line item with a check box to apply it to your purchase.
Check your quarterly balance and see your current valid certificates (if any) by using a desktop browser to go here:
https://reward.ebay.com/rwdwebui/bucks/myebay/main
