Error received when try to activate Identifier First

Problem Statement

We can not activate Authentication Profile > Identifier First. We get this error message: Only available for New Universal Login experience. However, New Universal Login is enabled.

Cause

When the Login page is customized, it automatically overrides the new ULP to Classic ULP. That is the reason for getting the error ‘One or more pages are using custom HTML to override the Universal Login experience.’

Solution

Please disable the customization for the login page because the Identifier first flow only works with the new Universal Login.