We implmented the REST API version of PayPal on our website about 3 weeks ago.
Most customers seem to be able to use it but now it seems that people using recently updated Mac's are not able to use it. The pop up box appears and ht ecircle spins but something blocks the form from appearing.
When we first installed this version we did find a confilct with the Security Content Headers that we are required to have in order to be PCI compliant. We seemed to resolve this by adding script-src https://www.paypalobjects.com style-src https://www.paypal.com;