Newly created user with "Administrator role" cannot access Plesk or manage server settings.
Wrong User role or the email address is used as user name for logging in to Plesk.
Go to Subscriptions > Users tab > click the needed user and make sure that Role is "Administrator".
To change user role use "Change Settings" option and change "User Role" to "Administrator"
Note : username for logging into Plesk is set by default as the email.
To change "Username" for logging into Plesk please change it as shown on the example below: