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Tripti LakharaTripti Lakhara 

We couldn't find a user's successful login using multi-factor authentication. Make sure you successfully log in at least once and that you are prompted for a second form of authentication.

In Trailhead unit:
User Authentification > Secure Your User's Identity

Cannot find error to complte Challenge.

I completed the Challenge succeeding at all steps:
1. Setup> "Session Settings", "Two-Factor Authentification" is in "High Assurance" category listbox, saved.
2. Created new user with "Salesforce Platform License", Profile as "Standard Platform User":, Generated new password.
3. Created new permission "Trailhead", in "Session Permissions", edited to select "Two-Factor Authentification for User Logins", saved.
4. Went to "Manage Assignments", assigned permission set to new user's account, Add Assignment, clicked Assign.
5. Successfully connected Salesforce Authenticator Mobile App to the user account:
6. I logged out of Salesforce under my name and logged in with new user name, followed steps and succeeded to use 2 factor authentification with mobile to log into Salesforce. Numerous times.

Clicked on "Check challenge to earn 500 points" and receive error notice and get message:
"Could not find a user's successful login using two-factor authentication. Make sure you successfully login at least once and that you are prompted for a second factor of authentication."
 
SwethaSwetha (Salesforce Developers) 
HI Tripti,
Please note that Questions about how to pass Trailhead challenges are not on topic, because these challenges are intended to be independent demonstrations of your abilities.

Trailhead Help (https://trailhead.salesforce.com/en/help?support=home)can provide assistance for situations where Trailhead does not appear to be functioning correctly. You can reach out to them if this is the case.

If this information helps, please mark the answer as best. Thank you