Usability Request: invalid card number feedback

[burnto]

From @larsperk's https://github.com/paypal/PayPal-iOS-SDK/issues/122

When the user enters a credit card number which is invalid, there is no feedback provided other than the "Done" button is grayed out and card number turns red. There is plenty of real estate below the fields to display a message clearly alerting the user to the problem when the focus changes.

[burnto]

Hi @larsperk - we'll discuss and respond back here.

Note that we haven't seen other reports of this validation as a usability issue, and we would like to keep the UI relatively simple and free of cluttering messages.

[andyzei]

This is an issue that several of our customers hit as well, just FYI