Challenge not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Update failed. First exception on row 0 with id 001o000000YgPyRAAV; first error: FIELD_INTEGRITY_EXCEPTION, There's a problem with this country, even though it may appear correct. Please select a country from the list of valid countries.: Shipping Country: [ShippingCountry]

this is the one that updates contacts mailing address when the account shipping address is changed.