One Subscription can ONLY transfer ONCE!
You must purchase the transfer under the same user account (same email), with the device you want to transfer from.
After your payment is clear, you will receive an Email with the instruction about how to do the transfer.
Please check your email, including the Spam folder.
This is a one-time fee that cost you each time when you want to switch to a new device. Your subscription will still be the one you purchased, it’s just the device is the new one.