Is the seller religiously obligated to pay the currency difference to the buyer after the bank converted the value of the shares from dollars to Yemeni riyals without the knowledge of both parties at the time of sale?

Selling shares has three scenarios: The first is before the project commences, and its reality is the exchange of cash for cash. Simultaneous possession and equality are required if the currency is the same. The second is after all the money has been consumed in the project, and its reality is the exchange of goods for cash, requiring the conditions of sale to be met. The third is after some of the money has been consumed and the remainder is still cash (a date mixed with dough). Jurists have differed regarding its ruling, oscillating between invalidity and permissibility. If you sell your shares in the bank before the activity begins, the requirement for equality and simultaneous possession depends on the currency being the same. If you sell them after some of the money has been consumed in goods, the transaction is invalid according to the majority of scholars, but permissible according to the Hanafis. It is not permissible for your counterpart to demand a currency difference after the sale has been completed.