Looks like Paypal might have changed something on their end that is causing user upgrades to not complete. Not sure if anyting on XF side would need to be updated. One person found a workaround by add a shipping option to the code for the button to work. Here are two threads that I found about it.
www.paypal-community.com
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Paypa
The legacy button form just started having issues yesterday afternoon. Users are all saying that at the "PayPal checkout" page, when they click complete purchase, nothing happens.. the button is unclickable. Help? I'm assuming paypal changed/broke something.. code is the standard: <form......
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