Things don’t appear to be working at the moment.

When a customer tries to buy more than one product they get Paypal redirection error “Things don’t appear to be working at the moment. Please try again later” It works fine for a single product or multiples of a single product, just can’t buy different items and checkout. The only thing I can find about it is Paypal has updated its systems on 29th March 2017. Any webform which is used to accept payment via Paypal Standard payment gateway should have “Billing Address” field on it. Make sure you have the field added to the webform and then place it on the checkout page. I can’t see a way to add the Billing Address field in Ultra Simple Cart. Is there any fix for this?