I'm trying to complete this trailhead challenge, but keep being notified that the rules don't check out. That doesn't seem to be the case when I attempt to change the Mailing Postal code on the contact record. Not sure what I could be doing wrong here.
Here's my validation rule formula:
AND( NOT(ISBLANK(AccountId)), NOT(ISBLANK(MailingPostalCode)), MailingPostalCode != Account.ShippingPostalCode )