Strong Customer Authentication (SCA) is a new European regulatory requirement to reduce fraud and make online payments more secure.

We run our payments via Stripe.  Now SCA is required by Stripe  -- this means to accept payments and meet SCA requirements, we build additional authentication into our checkout flow. 

We now use 3D Secure 2—the new version of the authentication protocol rolling out in 2019—will be the main method for authenticating online card payments and meeting the new SCA requirements. 

Applying 3D Secure typically adds an extra step after the checkout where the cardholder is prompted by their bank to provide additional information to complete a payment (e.g., a one-time code sent to their phone or fingerprint authentication through their mobile banking app).