Please Help me in resolving this error.

@Prapti Saxena

- Check the below code 

trigger AccountAddressTrigger on Account (before insert, before update) {
    for (Account acct : Trigger.new) {
        // 1) Skip every record where the checkbox isn’t checked
        if (!acct.Match_Billing_Address__c) {
            continue;
        }
        // 2) On update, only act if it just flipped from false → true
        if (Trigger.isUpdate) {
            Account oldAcct = Trigger.oldMap.get(acct.Id);
            if (oldAcct.Match_Billing_Address__c) {
                // it was already true before, so skip
                continue;
            }
        }
        // 3) Now we know Match_Billing_Address__c is true (newly checked or on insert)
        //    and we can safely copy the Billing postal code over
        acct.ShippingPostalCode = acct.BillingPostalCode;
    }
}