You cannot use an Amazon gift card balance to buy other third-party gift cards.
If you need an eBay gift card, you should use official or authorized channels to avoid scams: Specialty Gift Cards - Amazon Customer Service can i buy ebay gift cards on amazon
Amazon explicitly prohibits using your gift card balance to purchase "certain third-party gift cards" to prevent fraud and money laundering. ✅ Where to Buy eBay Gift Cards Instead You cannot use an Amazon gift card balance
If you find a listing for an eBay gift card on Amazon from a third-party seller, be extremely cautious. Even if you could find one: can i buy ebay gift cards on amazon