Bought the USPS label from Amazon but lost an A-to-Z Claim

I lost an A-to-Z claim for an FBM because the item got lost (and still delayed after 30 days in the USPS system). The buyer filed the A-Z and won.

I bought the shipping label from Amazon directly and shipped it within 24 hours. I always thought the seller is protected from these types of losses/claims when we buy the USPS labels directly from Amazon? Did I misunderstand the policy?

I filed an appeal and lost the A-Z. I no longer see a way to appeal the decision. Any thoughts?