We did this offer several years ago and at that time they accepted a photocopy of a mailer. You must be a new club member to use it. I would go prepared with a photocopy. If they confiscate your mailer or voucher from another casino, you can always try getting a replacement copy from the casino you got it from by asking a host or slot club. Island View also was pretty generous with follow up mailers after I played the free play (plus more) through and continued mailers for awhile even when I just did follow up free play (in diminishing amounts).