Unable to sign-in IAM User

It appears that you're encountering a common issue when trying to sign in with an IAM user created through IAM Identity Center (formerly AWS Single Sign-On). The problem is that you're attempting to use the standard IAM user sign-in page, which is not the correct method for IAM Identity Center users.

When you create a user through IAM Identity Center, the sign-in process is different from that of a standard IAM user. Instead of using the regular IAM user sign-in page where you enter the account ID, username, and password, IAM Identity Center users need to use a specific access portal URL to sign in.

To sign in with your IAM Identity Center user:

1. Use the access portal URL provided in the email invitation you received when the user was created. This URL typically looks like: https://d-xxxxxxxxxx.awsapps.com/start

2. If you don't have the email, ask your AWS account administrator for the correct access portal URL.

3. Go to this access portal and sign in with the email address and password you set up for this user.

4. After successful authentication, you should see the AWS accounts and applications you have access to.

5. Select the appropriate AWS account to access the AWS Management Console.

The fact that you can log in using the mobile app with the QR code suggests that your credentials are correct, but you're just using the wrong sign-in method for console access.

Remember, IAM Identity Center users cannot use the standard IAM user sign-in page with the account ID. They must always go through the access portal specific to your organization. If you're still having issues after trying this method, double-check with your AWS administrator that all permissions and account assignments have been correctly set up for your user in IAM Identity Center.
Sources
Unable to Sign in to AWS Management Console with New User | AWS re:Post
Trouble accessing/logging in to new account | AWS re:Post