- Download https://curl.haxx.se/ca/cacert.pem
- Rename it api_cert_chain.crt
- Copy to PROJECTDIR/plugins/prestaPaypalPlugin/sdk/lib/PayPal/cert/ (overwriting the existing file with the same name)
Alternately, you could do it in your code. Download cacert.pem and directly set the path to it in the code. Something like this:
$caller =& PayPal::getCallerServices($profile);
$caller->setOpt('curl', CURLOPT_CAINFO, '/PATH/TO/cacert.pem');
Note that you cannot fix by updating the path in php.ini because presta overrides the php.ini default with PROJECTDIR/plugins/prestaPaypalPlugin/sdk/lib/PayPal/cert/api_cert_chain.crt in PROJECTDIR/plugins/prestaPaypalPlugin/sdk/lib/PayPal/CallerServices.php:
function CallerServices($profile)
{
...
$this->setOpt('curl', CURLOPT_CAINFO, dirname(__FILE__) . '/cert/api_cert_chain.crt');