In sandbox, 3D Secure is automatically enabled for all merchants.
In production, 3D Secure is not automatically enabled in production accounts and is only compatible with certain Braintree configurations in specific regions. Contact us if you're interested in 3D Secure. We can help determine if you can use 3D Secure and if so, enable your production account.
Merchants based in the US must complete additional setup and integration steps to successfully process with Amex SafeKey. If you haven't already, you'll need to contact us first. You'll find the changes necessary for Amex SafeKey in the client-side guide and important considerations for liability shift.