If you created an account with Google SSO either through FullContact for iOS or FullContact for Web, you will be unable to sign in using that method for FullContact Card Reader, because we do not store Google passwords.
To fix this, you would need to get a password created by using the Forgot Password feature or login to your FullContact Web App account and go to My Profile page where you can setup a new account password. Here just enter your Google password as the Old Password and enter a new password that will also work with your CardReader App.
OR you can go to the following link: https://app.fullcontact.com/login/ and click on Forgot Password?
Then enter your FullContact account email address. This will kick off the password reset flow so you can create a password for your FullContact account, which you can then use to sign in to Card Reader.
If you are already signed into FullContact for Web, go to the following link: https://app.fullcontact.com/#/profile
Then click on Change Password, then Can't remember my password? This will initiate a password creation process so you can then create a password for your account.