Issue
You receive the below error when trying to process an order via PayPal over Braintree:
"error":"2fa_required","error_description":"Unable to authenticate the user."
This error is triggered because the old checkout.js version from Braintree does not support the two factor authentication for the PayPal login.
Resolution
By switching the authorization method to Widget authorization
within the payment method configuration you can
enforce using the newer version of the checkout.js
from Braintree. However there will be a separate page
for displaying the checkout form.