Hi
Muse paypal widget uses the ID which you setup on Paypal end. Paypal widget is tied to the ID , so whatever service your ID is using, users will be redirected to that payment page.
As such from Muse we cannot setup Payment Gateway, but yes you can do this setup from your hosting platform. Configure payment gateway and then you can use the payment process for product purchase. From Muse we are only sending paypal information that which account should receive money.
If you are using Adobe hosting , please let me know.
Thanks,
Sanjit