This happens if the email or browser you're using doesn't support opening the app directly. You'll need do the following steps to set your pin:
Click 'Set Pin' from your email
Click 'Already installed'
Click 'Sign In to Wagetap'
If it doesn't take you directly to the app, you'll need to open the app and press the 'log in' button for 2 seconds
Follow the instructions on the webpage and copy/paste your credentials
You're ready to connect your bank account