I have pasted the URL correctly but why I'm I getting this??

Hey Lateesh, 

I see this issue being reported elsewhere too.

The resolution found was to deactivate the Account Validation Rule.

However you can consider the following.

Your Trigger is Active. 

If you have other triggers on Account, please mark them Inactive

If you have any Active Validation Rules on Account, please mark them to inactive.

After you have verified this all, please try the code below & Check challenge.

trigger AccountAddressTrigger on Account (before insert, before update) {
    for(Account a : Trigger.new){
        If (a.Match_Billing_Address__c = true && a.BillingPostalCode!=Null) {
            a.ShippingPostalCode = a.BillingPostalCode;
        }   
    } 
}