Media for Firewall settings to allow HTTPS connection to perl script?

Firewall settings to allow HTTPS connection to perl script?

I have a problem with a shopping cart not working with a payment service provider. The shopping cart is hosted on a 3rd party webserver, the payment service provider on a different HTTPS server. The shopping cart is on a non secure webserver as no confidential data is transferred to the HTTPS payment service providers site.

This is the process

1) HTML shopping cart on an HTTP site sends post with order details(ie amount,order number), and the a return script url (on the cart site) to HTTPS payment service provider.

2) The HTTPS service provider then sends the order details to the Perl script on the cart server.

3) The perl script on the HTTP cart site needs to send the data back to the HTTPS as confirmation of connection.

4) The HTTPS then sends confirmation of payment to the HTTP site's perl script.

5) The HTTP shopping cart records that the goods have been paid for.

The process for me seems to be breaking down from step 3.

Can anyone say what firewall rules and Ports would need to be open to allow this to happen?

As I understand it people have said port 443 would not need to be open on the shopping cart server, but i thought as the initial connection was from the HTTPS site to the script on the shopping cart server, port 443 would need to be open to incoming traffic?

Many thanks Pete