Plugin support recurring payments. PayPal team checked it for internal customers several time. Please check if you have other Braintree plugin with old braintree kernel library. Remove it from plugin folder.
Read this topichttps://www.foxnetsoft.com/documentation-braintreedropin#q3
1. Did you create the Plan in braintree admin mode and used nopcommerce product ID as plan ID?
2. Can you tell me if I understood you?
a) Customer opened the checkout in nopcommerce.
b) Customer saw Braintree widget and used sandbox credit card and pressed the button ''Submit payment '
c) Customer saw order confirm page (checkout step) and pressed the button 'Conform order'.