How to cast videos from phone (HBO Go app) to a smart (non-Android) TV?

Can you tell me how, please?

My phone runs Android 6.0.1, and my smart TV is Grundig (non-Android). I can do this in Youtube app, and in Netflix app, but not on HBO Go.
I have installed Google Home (Google Cast) app, but there isstill no button inn HBO Go. And Google Home says that there is no compatible devices to cast screen to.

All tutorials I have seen are outdated.

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