If your email account supports 2-Step Authentication, then AltaMail will present a web page with a login for your email account. Login to your account when the login web page appears.

If you get an error logging in, check that you are logging in with the correct email account to match the title bar.

Also check that you have enabled the "Use 2-Step Verification" setting in the edit account screen - Settings section. View

When you create a new email account that supports Use 2-Step Verification, you do not need to enter your password. Enter your email address and tap on "Use 2-Step Verification" in the bottom of the new account screen.