I'm not sure if you're writing in the context of Payflow Pro or in terms of PayPal in general. ie: which one are YOU using?

Zen Cart v1.3.9 is fully compatible with the new PayPal/Payflow/Payflow Pro requirements.

Zen Cart v1.3.8 can be patched for compatibility (details will be posted next week), or you can upgrade to v1.3.9 when it is released.

Users of Zen Cart v1.3.7 and older will not be able to use the free addon for Payflow Pro because the addon is not compliant with the new Payflow Pro requirements.