Dropbox adds mobile prompts for two-step authentication, here is how they work0
For example, there are times that network coverage is not good enough to allow you to receive text messages so that you can log in to your Dropbox account using two-step verification. This is especially troublesome if you don't keep track of emergency backup codes provided to you by Dropbox, or when you don't have the two-factor authentication code generator with you.
So, starting today, Dropbox customers can use the mobile application to verify their identity. Every time you sign in, you can set up the mobile app to receive a notification on your phone so that you can simply tap a button to finish the login process.
The new two-step authentication method seems like a great new feature to replace the notification via text message option. It also comes in handy since it works even when you don't have cell signal because you can use Wi-Fi connectivity instead.
In order to access mobile prompts for two-step verification, you can click the “Having trouble getting code?” link after entering your email and password on the Dropbox website. It's also worth pointing out that the new feature is available on both Android and iOS devices.