Ubiquiti requires any 3rd party guest WiFi system, such as Fydelia, to have direct access to the controller in order to be able to authenticate devices. Fydelia is not permitted to connect to your controller via the “unifi.ui.com” route.

Therefore this requires the creation of:

• A firewall rule on the UDM to allow external traffic on port 443 into the gateway
• A local admin account with remote access disabled

To allow connections into your UDM Pro follow this guide

To create a local admin account follow this guide

For security you can restrict access with IP locking using these IP ranges. i.e. no human access

You can find the complete setup guide here