MAC based authentication is used in conjunction with a RADIUS server.
https://documentation.meraki.com/MR/Encryption_and_Authentication/Enabling_MAC_based_access_control_...
I didn't realise you can't use a sign on page as well - but it shows that in your screen shot.
If is more common to use WPA2-Enterprise mode. Typically companies authenticate this against Active Directory using the Microsoft NPS service. You should be looking at this option.
https://documentation.meraki.com/MR/Encryption_and_Authentication/Configuring_RADIUS_Authentication_...
You can also use WPA2-Enterprise mode with Meraki Authentication, were you create accounts for users in the portal, but you would only want to do this if you had a small number of users.
If their is no centralised authentication like Active Directory you can also use Meraki Systems Manager using the Sentry option where it deploys certificates onto the devices. This can have a whole lot of pain, so your specific environment would need further consideration.
https://documentation.meraki.com/SM/Deployment_Guides/Systems_Manager_Sentry_Overview