Biometric authorization is a convenient shortcut to authorize payments and view your balance in PAI Up, but it is not a strong security solution.
To ensure the majority of your funds are safe in the event your phone is stolen, PAI Up sets a limit to the amount of value that can be sent with only a biometric identifier. If you or anyone else tries to send more than that limit (accumulative), your wallet passcode will be required.
You can change the limit by choosing Fingerprint/FaceID Authorization Limit in the PAI Up settings.