GL-MT300N-V2 Chromecast?

Ok so i set the box up and loaded my ovpn which works.
Problem now is with all my devices connected via WiFi I can’t cast from one to the other. I assumed I would be able to do so.
Is there an option or setting in the webUi to help my acheive this?
I can’t seem to find any info on this online.

You need to connect other devices you want to cast to the mini router as well. All the devices should connect to one router.