Question [Q] Paypass/paywave through a case

Hi All,

I couldn't find this through searching on the forum but sorry if it has already been asked.

I currently have a Z2 with the roxfit book style case (similar looking to the official sony book style case but with a slot for a card). I have a credit card with paypass on it (contactless payment) and have tried to use it with the case closed once but the terminal didn't accept the transaction. I tried again with just the case flipped open and it worked that way.

Does anyone know why this is the case (or if it should be working)? I'm thinking it has something to do with the nfc chip inside the phone (although deactivated) or the aluminium around the phone?

Thanks!