No RADIUS Server
Meraki has an option to allow access to the network by MAC addresses of machines. However, for large scale deployments, it's typical to use a RADIUS server for it. If your client doesn't have a RADIUS server to use, there is actually another way of doing it.
This is the link: https://documentation.meraki.com/MR/Splash_Page/Using_a_Sign-on_Splash_Page_to_Restrict_Wireless_Access_by_MAC_address
Long story short, you allow users to log in using Meraki authentication, and then allow those users to bypass the splash page if they have a Mac Address in the white list.