How is the value of the dollar determined when paying Zakat, given the multiplicity of exchange rates (official, banking, and parallel market), knowing that the dollar is only available in the parallel market?

Zakat is obligatory on paper currency if its value reaches the lower of the two thresholds (nisabs) for gold or silver, which is equivalent to 595 grams of silver. It is permissible to pay Zakat using the same currency or its equivalent in another circulating currency. If the exchange rate varies, it should be estimated at the highest possible rate, out of consideration for the rights of the poor.