I attempted to use PayPal to subscribe to the Akeeba Pro, but after clicking on PayPal button got:
"Unable to process payment. Please contact the merchant as the shipping address provided by the merchant is invalid, and the merchant has requested that your order must be shipped to that address."
All I entered for address was my actual physical home address in the USA.
And my normal email (not using it here as it might be seen as SPAM - (firstname.lastname@example.org).
May I also ask, are you using CSUBs for subscribership? Am investigating - kind of looks like it.