PayPal does not accept some requests if the HTTP/2 protocol is used. They are resolving this issue right now.
But as a quick solution, you can do the following:
Open the file system/library/paypal/paypal.php
Find the line CURLOPT_TIMEOUT => 10
After it, add the line CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1
There's an issue with this module at the moment, really needs an urgent fix.
Others have reported it too here: https://www.opencart.com/index.php?route=marketplace/extension/info&extension_id=38358