If you can watch some of it (trailers), then you should be able to watch the rest as well.
Be sure to sign in to the Apple TV app on your TV, through the in-app Settings, with the Apple ID account that has the Apple TV+ subscription linked to it.
If you already did that, then a next step is to see if there are software updates available for your TV. Install that, if available. How to perform a software update on your TV - Sony Support
Next, try these suggestions from Sony Support: YouTube, Netflix, or another streaming app installed on my TV doesn't work - Sony Support
If the issue persist after that, please ask the Apple Support staff for assistance. Contact Apple for support and service - Apple Support