You can purchase it through the authormedia.com website, which will take you to a gumroad downloading and payment service. To save time, however, here is the link. https://gum.co/mbtpro3. Purchase it there.
Gumroad will give you the license needed to use on the site. It will show right after you purchase, and it will show up in your email inbox, as well.
To make your updated plugin work, download and add to plugins on wp plugin dashboard on your website. Unzip like any other added plugin you purchase.
Activate and go to MBT settings and add new license key and then it should be active.