Expresso Store and PayPal

I have a site running EE 2.8.1 with Expresso Store 2.3.1. The recent TLS 1.2 PayPal upgrade has caused PayPal Express payments to fail - giving the error - Sorry, there was an unexpected error communicating with the payment gateway.

Is this being caused by the Store code? I need to determine if the issue is software or server related. Any help will be much appreciated.