Unfortunately, we have bad news for those who want to use UniFi Dream Machine Pro, UniFi Cloud Gateway Ultra, or devices with similar software as controllers: Powerlynx cannot work with such devices due to their software restrictions. We contacted the Ubiquiti support team to get more information, and they confirmed that it is not possible to use the UDM as an external port with a splash page hosted on a third-party site.
However, we have successfully tested UniFi APs connected to MikroTik controllers via VLAN or non-VLAN interfaces. Please, follow this topic to get more information how to connect UniFi AP to MikroTik controller: MikroTik controller with AP connected via VLAN interface.