Check the sender and receiver
Google recommends connecting the device sending the video and the Google Cast receiver to the same home network. Use an app that offers Cast and confirm the receiver is available on the television. On a Google TV device, Google’s help also shows how to check the Cast system app, update the device and restart it. Try a second Cast-enabled app before changing router settings.
Locate the failure in two steps
A missing receiver in every app suggests discovery is the immediate problem. Compare the actual network names and whether either device is on an isolated guest network. A receiver that appears and connects before the stream fails has already passed discovery. Test one source known to play on that receiver and record what happens when the receiver starts playback.
Treat app casting and mirroring separately
An in-app Cast session has its own playback path and controls. Your ability to play a stream on the phone does not establish that the TV receiver can play it. Record the phone, receiver, app and programme. If only one app fails after it connects, check the publisher’s receiver and format support before buying new equipment.