How can I get this so I can watch rentals? I tried to play a movie and got this: This movie can be played only on displays that support HDCP (High-bandwidth Digital Content Protection).

For MacBook Air, you shouldn’t get that message with an unmodified internal screen and no interfering software or peripherals. If you connect an external display, then the connection may cause HDCP issues. If you have certain Mac peripherals connected, then those might interfere. Try disconnecting what isn’t needed at that time. If you have screen capturing/screen sharing/etc. software active, then that may block the protected content. Try not running that software.

If you did everything right and still get the error, then your Mac software may need some troubleshooting.

Try to repeat it when started up in safe mode.

Try to repeat it when started up in another user account.