403 error on test challenge submit.

[Faizan-Shakeel]

I am testing ChallengeShopper flow using the helper functions in documentation,
const perform3DSChallenge = (responseData) => {}

On clicking "Pay", page reloads and iframe opens "Please authenticate (Challenge simulation)
".
I enter "password" in password input field and submit, iframe does not close, flow breaks and in the network tab, column time is "Pending" with status 403.
On clicking the link "https://pal-test.adyen.com/threeds2simulator/acs/challenge.shtml" in initiator column I get:
Challenge Failed
No creq, answer or acsTransId present

Whats missing?