The live stream is locked to the first device that you view it with.  If you need to switch devices, you must first unlock it using the link below the live stream itself.

If you can no longer access the live stream, you can reset all devices by logging into your Prekindle account.  Find your recent purchase in the list, and click the link to "Reset live-stream devices"

Next, click the reset button.

Finally, return to your email receipt, and click the button to view your live-stream again.