How many devices are supported under one license? What does the Devices Remaining mean?

With one license/account, you can use the Immerse Gamepack FFXIV edition app on up to 5 devices. To use your profile on other computers, you will have to download the Immerse Gamepack app. You can download the latest version from here, click on 'I have a license,' and enter the purchased license code. It will automatically pull your profile to that computer.

You can check the 'Number of devices remaining' on the Immerse Gamepack app.