Scrip

A scrip (or chit in India) is any substitute for legal tender. It is often a form of credit. Scrips have been created for payment of employees under truck systems, and for use in local commerce at times when regular currency was unavailable, for example in remote coal towns, military bases, ships on long voyages, or occupied countries in wartime. Besides company scrip, other forms of scrip include land scrip, vouchers, token coins such as subway tokens, IOUs, arcade tokens and tickets, and points on some credit cards. https://en.wikipedia.org/wiki/Scrip (airline reward miles?) (cf carnival cash, loyalty program, LETS)