The PayPal .NET SDK makes it easy to add PayPal support to your .NET web application and is built on PayPal's REST APIs.
The Payment Card Industry (PCI) Council has mandated that early versions of TLS be retired from service. All organizations that handle credit card information are required to comply with this standard. As part of this obligation, PayPal is updating its services to require TLS 1.2 for all HTTPS connections. At this time, PayPal will also require HTTP/1.1 for all connections. Click here for more information
Connections to the sandbox environment use only TLS 1.2.
General documentation regarding the PayPal REST API and related payment flows can be found on the PayPal Developer site.