If your Chromecast can connect to the Zyxel's wireless network, but no devices can talk to it (e.g. Unable to cast from laptop to the Chromecast):
- Log in to the Zyxel via IP address. (Open any browser and navigate to 192.168.1.1. The default username is admin and the default password is 1234.)
- Under Settings > Network > WAN, most of the way down the page, you'll see Multicast Setup. The default is set to None. Change it to IGMPv1/v2.
- Reboot the router. It may take 3-5 minutes for the router to come back online.
If you are still experiencing issues after that, please don't hesitate to reach out!