On This Page 
    Step 4: Step-Up Iframe
    Initiate step-up authentication on the front end after you receive the response as
            discussed in Step 3: Payer Authentication Check Enrollment Service. Note that frictionless
            authentication does not require this step-up iframe step. This step is only for step-up
            authentication when the issuing bank wants to challenge the cardholder.
When a challenge is needed to prove a customer's identity, a JSON Web Token is returned
            to you that contains a step-up URL. You open an iframe where the access token to the
            step-up URL (also known as the endpoint) is posted. The iframe must be sized
            appropriately to enable the cardholder to complete the challenge. The iframe manages
            customer interaction with the card-issuing bank’s access control server. The bank asks
            the customer to provide identifying information. Once the customer completes the
            challenge, the process moves to validating the information that the customer sent.
Figure:
Process Flow for Step-Up Authentication
Best Practices
            These practices should be followed for this step to achieve optimal performance and
                to minimize potential operating issues. 
- When a transaction requires a challenge, according to EMVCo protocol, the challenge must be issued within 30 seconds of the Enrollment Check response. When more than 30 seconds elapses, the ACS times out.