PayPal is upgrading SSL certificates, connection types, and so forth, which is generally a good thing.  However, CentOS has a tendency to be a bit behind on just about everything and that includes the version of cURL that is bundled into the OS.

To test your CentOS machine (or just about any linux machine) to see if it’ll be compatible with PayPal’s new updates, run this command:

curl https://api-3t.sandbox.paypal.com/nvp

If you get an SSL Error (35), you’ll need to run some updates.  If you get a long string back from PayPal complaining about the method not being supported, then you’re in good shape.

To get CentOS to actually use a modern version of cURL, there’s some great instructions here http://serverfault.com/questions/321321/upgrade-curl-to-latest-on-centos that worked perfectly for me.