Mat_Version3,
Under the Wireless > Monitor > Air Marshal > Configure page, scroll to the bottom and you'll find SSID alerting, From here, you can Add a match to any SSIDs you wish to be alerted for when a Meraki AP detects a spoofed SSID.
Please note that "rogue or Other SSIDs matching these rules (but not a rule in the SSID Allow list) will trigger an email or syslog alert, if configured. Meraki won't prevent clients from connecting to these SSIDs."
Don't forget to hit Save!