Pay later in Paypal sandbox displays json in window after clicking on pay now, how to fix?

[olansimal]

I'm attempting to integrate PayPal smart buttons. All works fine in the sandbox with the exception of pay later. When I click on pay later, login and choose to pay now, json is displayed in the paypal popup window (see below).

However, using the same sandbox account on the PayPal demo it works fine.

I can't find very much information on this at all. I'm using server side code to create the order and capture the payment, works fine for everything else.

Do I need to anything specific to handle pay later?

[A_Abbass_01]

You don't need to integrate differently for Pay Later. If the other buttons work, Pay Later will work. If testing Pay Later is not working in sandbox that's a sandbox testing issue, not a live/production issue.