Originally Posted by baliktad

There are two kinds of vouchers AS distributes.

1) A 'DISCOUNT CODE'. If your voucher is one long string of letters and numbers (usually starts with EC I believe), it's a Discount Code. Only one Discount Code may be used per purchase. Discount Codes may be for a fixed amount or percentage ($50 off, or 5% off), or might apply some other benefit (the AS Visa companion fare is basically a Buy One, Get One Discount Code). Discount Codes are single-use, like a coupon. Once you use it, you can never get it back. If you cancel a ticket for which you used a Discount Code, you will lose the Discount Code.

The distinguishing feature of Discount Codes is that they alter the base fare, before taxes and fees are calculated.

2) A 'CREDIT CERTIFICATE'. If your voucher is a 16-character code with a separate 6-digit PIN, it's a Credit Certificate. Up to 4 Credit Certificates may be used per purchase. Credit Certificates are a declining-balance value store, much like a physical gift card. If you don't use the entire balance, you can apply the remainder to your next purchase. If you cancel a ticket from which you used a Credit Certificate, you will get a Credit Certificate back.

The distinguishing feature of Credit Certificates is that they are accepted as a form of payment, so apply to the fare as well as any taxes and fees.