This message just occurred as one of my customer tried to checkout with paypal express. Saw the error message under abandoned checkouts.
Seems like there are other instances of this exact issue with other users. Like in here
Shopify, please fix this
I am having the same problem. I have been on customer support with Shopify and PayPal, yet no one can help as they can’t seem to find any issues. Having now found out there are others having this problem, there obviously IS an issue. Shopify please sort this out quickly, I have lost customers from this error.
I agree - terrible service from paypal or shopify