To log in with BankID, you need to have a personal identification number linked to your account. This can be added under 'My Profile' on 'My Page'.
Follow the instructions in this article to add your personal identification number to your profile.
Please note that this requires the organization where you are creating your account to offer the BankID service. You can ensure this by navigating to the organization's 'My Page,' clicking on 'Sign in,' and checking if the BankID option is available to select.