Simoles (§) are the currency used by the kingdom. Sims use simoles for buying and selling items, paying their taxes, making donations, and generally transferring wealth. Item-for-item swaps, i.e. bartering, is rare in the world of The Sims Medieval and is generally only done by the merchant.
Simole coins are known to be made of gold, though it is possible the gold is mixed with less precious metals, as pure gold is soft and as such not great for coinage. The name "simole" is derived from the "simoleons" used in modern-setting The Sims games, and like simoleons they are represented with a § (section sign).
It is unknown if other nations and territories use the simole as their currency, although when not bartering they will pay the merchant in simoles.