As far as the Zen Cart software is concerned, if you're using Zen Cart 1.3.9h or 1.5.0 and have not changed the built-in PayPal code or added other PayPal-related addons then there should be no software-related issues.
BUT this is also a firewall change ... so ... I can't answer you about the hardware used in your hosting company's datacenter:
If your hosting company has set up custom firewall rules for PayPal, then they'll need to handle those things themselves using the info provided by PayPal. That's entirely outside the control of Zen Cart.
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