Verify the install route before a subscription
Record the model and system build. Check the app name and publisher in the store on the box. Verify which viewing input the player accepts. After setup, test a known source and record the resolution reported by the player alongside the TV's HDMI mode.
Diagnose a format issue
If the player works until a particular file or channel opens, try a control item. Record source format, audio track and display chain. Keep the test on the same screen so the result can be compared with the manufacturer and player documentation.