Drupal combined with Ubercart already has a Paypal WPS module. We need recurring subscription support, so we also added uc_recurring ([url removed, login to view]), which works well.
However, the problem is that the Paypal WPS module with uc_recurring only supports recurring on the first item but allows more than 1 recurring item to be added to the cart. This creates the problem that a user could checkout with 2 recurring items but only have 1 subscription setup.
Note: Paypal Express Checkout is not an option because it does not support recurring payments (to my knowledge).
The current scenario:
1. The user adds 2+ items to their cart (of which 2+ are recurring)
2. The user attempts to checkout and sees the message about recurring
3. The user will checkout anyway, make payment, and then expect that everything worked
4. Now we have a problem that we have only 1 item recurring, the rest are not, and we have to manually fix this situation (A lot of trouble and explanation that the buyer really doesn't care about)
IDEAL SOLUTION: Implement full cart upload support for all recurring items in the cart
SECONDARY SOLUTION:* When a customer adds multiple subscription products to their cart, THEN the paypal option is disabled (with a message up top explaining).
*If it is not possible for the ideal solution, we would be open to alternate bids on the secondary solution and would consider listing a separate project for it. First, though, we would like to see if anyone can provide the ideal solution.