C If you wish to change the satoshi/byte please top up your card on the web app and not on the mobile app.
https://my.bitwala.com/ As a matter of fact I was going to ask you that question. I only see that option on the send money.
I can top up the card from here
https://my.bitwala.com/bitcoin?
It would be a good solution. Where can I find my card address?