First, make sure the phone, tablet, computer, or TV is not muted.
Next, try playing another video and check if the issue is affects just one specific video or multiple videos.
Then, try the basic troubleshooting steps here.
If watching on an older Apple TV, see some troubleshooting tips here.
If you are still having audio issues, please let us know at firstname.lastname@example.org and include your sign-in email, plus the device you are using and we will take care of the rest!