There are 3 ways you can sign in to your account and it depends on the first time you have signed up with ShopBack. :)

1) If you signed up for a ShopBack account using an email address:
Select 'Use email address'.
Enter your email address and password and click 'Sign In'.

2) If you have signed up for a ShopBack account with Facebook:
Select "Continue with Facebook".
Enter your Facebook email address (or phone number) and password and click 'Sign In'.

3) If you have signed up for a ShopBack account with Apple ID; 
Enter your Apple ID and password and click 'Sign In'.