Hi TW,
Welcome to Centrify Community!
There are various reasons to cause 'Network Unavailable'. One of the reason is blocked by user policy.
Here is the example:
Beside 'invite based enrollment', would you please confirm if you have permitted device enrollment? It is suggested to check all items listed in 'Device Enrollment Settings' policy. In addition, would you please check client app settings to see login URL? Please modify to 'https://cloud.centrify.com" if this is different. If it still not working even everything is configured nicely, please try to enroll on other device using the same user account to see if this is device problem (ie. network issue or proxy)?
Hope this will help.
Kind Regards,
Yeny