urrency on Thar Shaddin is not the usual copper-silver-gold system or printed money. It was discovered shortly after the magical explosion of the Changers' War that gold was one of the first things that began to get produced by mages. For obvious reasons, anyone who could figure out how to manipulate matter to create gold or silver did so. Combined with the complete chaos of the War, standard monetary systems became worthless and for a long time it was militaristic rule, slavery, and the barter system that governed who had wealth.
Once the war had subsided and Pal Tahrenor came out of its dark ages, it became apparent that society would have to find a structured monetary system that would be hard for mages to take advantage of. What was settled on was the Bishan (plural Bishani).
Bishan, in the native language of Thar Shaddin, translates to soul or energy. A Bishan consists of a small coin about the size of a penny, but rather than metal they are made of a translucent green crystalline substance that contains a magical signature unique to the factory of its creation. There are only five factories on Pal Tahrenor, all created by gnomes and some of the greatest magical minds around and located across the continents you would call Europe and Asia.
Forging Bishani is possible, but it's nearly impossible to do perfectly. Many mages from many races have the ability to feel the magical imprint on a Bishan, and skilled readers are exceptionally good at identifying a forgery. The signature is so complex that forging just Bishani would take the average mage at least a year or two of practice, and each one would be an effort in itself. In the end fake Bishani, usually just made out of glass, do circulate, but nobility and governments always employ a skilled reader to check their money.
1/4 Bishan, 1/2 Bishan, 1 Bishan, 5 Bishani, 10 Bishani, 50 Bishani
For the purposes of playing on Thar Shaddin, 1 Bishan is roughly equivalent to 1 dollar. The people are somewhat poor, and because of the setting and general lack of huge luxuries, most people never handle more than a few hundred of them. Average wage is about 150 to 300 Bishani a month.
Gold: Although gold can be forged, it is still rare enough to be considered valuable. It takes most people with conjuring abilities time and effort just to create or convert a small amount of something into gold. In the end it still needs to be mined and shipped just like on the real world. Thus, gold and other precious metals are still valuable. They're just not common currency.
Notes: Printed documents can be made and used as tender. Mages have ways of making documents hard to forge, and some people specialize in the skill. Think of printed documents like bank notes that only specific banks or rich people will recognize.
Precious Stones: Diamonds and other precious stones are also still valuable. Jewelery is still a luxury and people always like pretty things. The difference on Pal Tahrenor is that these things are slightly cheaper and more diverse. The value of the stone depends on who it's being sold to, what race they are, what society they live in, etc. Treat it like a barter system.