First you need to login to your JVZoo account. If you login to your seller account then you need to look to the top right hand side of the page and find the button which says "Looking for your purchases?".
Click on the button which says "Looking for your purchases?"
Next you will come to a page which looks similar to the one on the right hand side. You will need to scroll down the page and find where you purchased Magic Page Plugin.
Click on the button which says "view details"
On the next page you will see a box half way down the page titled "Your Purchase Details".
Look for the transaction ID which starts AP- and copy this into where your API Key would usually go.
Find the transaction ID similar to AP-XXXXXXXXXXXXX and use that as your API Key from now on