Braintree refuses to work

Hi, I bought the Braintree add on. I’ve already uploaded it and configured all the settings and API keys. But when you go to invoices there is no way to pay. If I select PayPal, then a pay button shows. But once I switch from payPal to Braintree as the credit card processor, the button goes away.

Please help!

https://www.ads-software.com/plugins/sprout-invoices/