Error: There was a problem connecting to the payment gateway.

this worked for me too.. i was having the same issue.. thanks so much!

It did not work for me either. Decided to download an archive copy of wordpress 4.3.1 and installed the ca-bundle.crt file copy from wordpress 4.3.1 and it worked. Not sure why his copy didn’t work for me. Hopefully, this will help someone else.

This problem reared it’s ugly head on our site too recently. Glad i found this thread, webaware’s link to the ca-bundle.crt worked for us. I just overwrote it on the server in /wp-includes/certificates/ and credit card payments via WooCommerce Paypal Pro started working again.