Guide for setting up multicast across vlans for Chromecast?

[FullyBorked]

I've been working with this on and off for a few months trying to move my Chromecasts into my IoT VLAN.  But try as I might I simply cannot get them working.  Does anyone know of a comprehensive guide to get these up and going?  I've setup MDNS Repeater, UPD Broadcast Relay, etc.  not 100% sure they are even properly configured.  But I just can't make this work.  So I'm missing some key step I would guess.  Doesn't help that I don't fully understand the communication with the Chromecast.

[MenschAergereDichNicht]

First of all i don't have a direct answer to your question.

But i do have a Chromecast in a separate VLAN network. I don't send the Chromecast traffic into the regular LAN. Instead i just use the IOT WLAN on the Chromecast control devices (mobile, tablet).
The downside is that i sometimes have to switch the network on my mobile.