You are doing it wrong, you are trying to Link Paypal to Zapier and that's completely wrong.
Since paypal can ONLY be linked to one platform (either Clickfunnels or Zapier).
thus you MUST do it this way:
Setup your Paypal integration with Clickfunnels the way it should be.
Connect Zapier to Clickfunnels (mostly using Webhooks).
When a purchase arrives through Paypal to Clickfunnels, Your Zap will be notified and your actions will get triggered.
that's the healthy way of doing it, as for trying to interfer with Paypal's logic isn't really recommended, and also Paypal itself only supports a single IPN which is CF's.
hope that helps!