Hello @Sk Sahed
Thank you for posting this concern on this community space.
I was reading your case scenario description and I would like to ask you few points below:
-Was this working properly before?
-Did you configure this Gmail accounts as external user account on the Azure AD?
-Did you try too many times? so your user account could be labeled as risky user sign-in..
-Did you try to log in using PowerShell in order to double-check if you are using the right credentials at least?
I hope that can be useful for you.
Looking forward to your feedback,
Cheers,
Please "Accept the answer" if the information helped you. This will help us and others in the community as well.