API does not handle card / charge errors

# Problem

We have just a match error for card declines right now. We should provide a more appropriate response to the user since there's no error handling specific to the card being declined at all.

```elixir
no match of right hand side value: {:error, %Stripe.APIErrorResponse{code: "card_declined", message: "Your card was declined.", status_code: 402, type: "card_error"}}
```