Your SSID is probably configured to authenticate using a certificate, so only machines that are in the domain can authenticate, as they have the certificate installed on the machine.
To resolve this issue, you need to install the certificate on devices that are not part of the domain manually.
I don't know if you have mastery of ISE, but it would be interesting to request support from someone who has good knowledge of ISE.
It's not complex at all, but you need to have a minimum of knowledge.
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.