I have the latest version (3.08.1) of WP-invoice installed on a new website that I am running through MAMP. The PayPal express checkout button is not displaying on the invoice page. I’ve checked the global settings and the Default Payment Method is PayPal and the PayPal Username is the correct PayPal account. I tried deactivating all other plugins and it still didn't work. I'd really appreciate any help on this?