They have the billing solution.
https://documentation.meraki.com/MR/MR_Splash_Page/Billing_for_Wireless_Access
It's not automated but is a option. If it's doesn't make sense for you, maybe you should have to go with a third party solution like splash access or Cisco ISE.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
Please, if this post was useful, leave your kudos and mark it as solved.
