In order to use Face/Touch ID or Fingerprint, you first need to enable it in your phone setting. For both iOS and Android, go to 'Setting', then select 'Touch ID & Password' for iPhone, or 'Security' for Android.
Next, turn on the ‘Remember me’ button on the first screen of the app. By enabling Touch ID/Fingerprint login, you are allowing anyone who has a fingerprint stored on your device to access your Merchant Account. Please review the fingerprints stored on your device and make sure all are authorised to access the Account information through the Amex Merchant app. You can turn these features on or off any time via the Account tab at the bottom of the screen.