I have researched this on the internet (including MarketPress Support) and see many exact issues, some dating back a couple of years. I can't seem to find a final resolution for MarketPress including this thread from 3 weeks ago: https://premium.wpmudev.org/forums/topic/i-receive-this-error-when-product-is-priced-000-and-shipping-costs
I set up a coupon at a discount of 100%. I'm using Table Rate Shipping. The objective is to offer the product for free but pay for shipping.
All is computed correctly
When I choose Pay by PayPal (using PayPal Express) I get the following message:
There was a problem connecting to PayPal to setup your purchase. Please try again.
10413 - Transaction refused because of an invalid argument. See additional error messages for details. - The totals of the cart item amounts do not match order amounts
Any guidance on this?