PayPal Redirect issue

I am guessing paypal changed something a few weeks ago.  my paypal orders are no longer being marked as paid and customers are receiving this error.  

nop3.6 using Payments.PayPalStandard

Server Error in '/' Application.
The request was aborted: Could not create SSL/TLS secure channel.

my SSL is good through July.  

where do i find the URL that paypal redirects to?
any other ideas as to where to look for resolving this?

thank you in advance

Before diving in too deep, check your server to see if it still supports TLS 1.0, 1.1 or anything less like SSL:  https://www.ssllabs.com/ssltest/

PayPal requires TLS 1.2 or higher, and will refuse connections if they detect those insecure protocols enabled on your server:
https://developer.paypal.com/docs/api/info-security-guidelines/#usetls12