Is it permissible for the seller to demand the price difference from the buyer if he discovers that he sold him goods at a lower price due to forgetfulness, after the purchase was made several times at the same lower price?

If the sale contract has been concluded and its session has ended, and the seller later claims that he made a mistake in the price he offered, the buyer is not obliged to pay an additional amount; because the contract was concluded fulfilling its conditions, and the seller bears the consequence of his mistake.