Hi Guyz,
Trailhead requirement for validation:
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Create a validation rule to check that a contact is in the zip code of its account.
To complete this challenge, add a validation rule which will block the saving of a new or updated contact if the contact is related to an account and has a mailing postal code (which has the API Name MailingPostalCode) different from the account's shipping postal code (which has the API Name ShippingPostalCode).
Name the validation rule Contact must be in Account ZIP Code
A contact with a MailingPostalCode that has an account and does not match the associated Account ShippingPostalCode should return with a validation error and not be saved
The validation rule should ONLY apply to contact records with an associated account. Contact records with no associated parent account can be added with any MailingPostalCode value. (Hint: you can use the ISBLANK function for this check)

Every time I'm getting the same error as ---  Challenge Not yet complete... here's what's wrong: 
The validation rule failed to enforce the business logic

My validation formaula is :
1) AND( NOT( ISBLANK( AccountId ) ), MailingPostalCode <> Account.ShippingPostalCode )

2) AND( NOT(ISBLANK( Account.Id)), MailingPostalCode  <>  Account.ShippingPostalCode )

3) IF(ISBLANK( Account.Id ), false, (IF(MailingPostalCode  <>  Account.ShippingPostalCode, true, false)))
4) AND( NOT( ISBLANK( AccountId ) ), MailingPostalCode__c <> Account.ShippingPostalCode )

My challengfe is not passing in for any case but its firing from frontend.