Braintree Plugin

hello
We bought the Braintree plugin in 2015 and it was working until middle of december 2018 but since that time the checkout creates a 500 server error, debug is not showing any errors everything else is working fine-
But i noted that this plugin is not anymore in your shop or somewhere else available.
any explaination would be nice.
many thanks in advance for some solution.
Dieter