Why is customer sign-up required when "Account Optional" is enabled?

Your third-party shopping cart may override the Account Optional setting through the API call to PayPal. You can bypass this cart restriction only by contacting the support team for the shopping cart to see if there's any way to alter the default API settings of the cart. 

If the card being charged has been used too many times for Guest Checkout payments, your buyer may be required to either: 

• Create a PayPal account. 
• Use a different payment method.

If you have any issues with your payment solution, contact our Merchant Technical Support.