Looks like eBay now have a tiered system for cashback (similar to Amazon).

Notes

As of 28th October 2019, Any purchases made with the use of Coupon / Voucher Codes are not eligible for Cashback

Any Purchases with the use of Voucher / Coupon / Promo code will result in cashback tracking at $0.00

Cashback Not Eligible for Gift card purchases, Charity and non-profit items, eBay Plus membership, Cars, Bikes, Boats , Coins, Real Estate, Services, Tickets, Travel

Excludes taxes, fees or additional extras

Only purchases made through eBay Australia will earn Cashback. Cashback is valid when gift cards are used as a payment method