As part of version 2.5.4 and beyond, Payment Plugins is now hosting the Pro version of Braintree For WooCommerce on their own servers. You will continue to receive updates to the plugin in the same way as always, but the updates will come directly from Payment Plugins.
Wordpress.org will be used to host the Free version of the plugin, which consists of all the same functionality but integrates with Braintree's Sandbox environment.
Ideally, after updating to 2.5.4+, you will be prompted to install the Pro version of the plugin automatically. As some merchants have their sites setup for automatic updates, they will not have this option.
You should download the Pro version HERE and install it on your Wordpress site. Deactivate the Free version of the plugin and then activate Pro. Your license will be automatically recognized once Pro is activated.