Payments > Subscriptions > Store > Paypal (How?)
Installation and Configuration
If you have the FoxyCart modules still activated, you should disable them since you won't need them if your using the new Payment modules.
I don't believe the new Payment modules show a success message like that when adding an item to the cart.
I'm not seeing an issue on my dev site.
Hope this helps!
updated by @douglas: 03/11/18 11:53:03AM