Why can't WIFI streaming devices in a guest network be set up/operated via app?

Setting up and controlling WIFI streaming devices in a guest network is generally not possible via the app.

Reason: In guest networks, communication between two or more network devices is generally not allowed. However, this communication is a prerequisite for setup/operation.

Solution: Set up the devices in a network that allows communication between the devices, e.g. their (normal) WIFI. If necessary, also check the settings in the router in this regard.