Payment Action of Authorization is not allowed with Unilateral and Non-Credentialed authentication
I got this problem when I use paypal express checkout on Magento 2.3. I tried to use sandbox. It seems run well. I can see the paypal login form popup and can login successfully. But after I click 'Pay' button and the popup is closed then I saw a flash error message on my Magento 2 site.
PayPal gateway has rejected request. PaymentAction of Authorization is not allowed with Unilateral and Non-Credentialed authentication (#10481: Transaction refused because of an invalid argument. See additional error messages for details).
Then I inspected the log file. I see the debug message but I have no idea what is wrong. Is this caused by Magento and/or paypal? Here is the debug message: