What is the ruling on selling silver items by deferred payment according to the gram price at the time of sale, and what should be done if the contract is impermissible, given that years have passed and the volume of sales is unknown?

Selling silver and gold for currency requires immediate possession (taqabud) at the session of the contract, and postponement is not permissible. However, selling them for other commodities (non-currency) allows for postponement. If silver was sold for currency without immediate possession due to ignorance of the prohibition, then nothing is incumbent upon you, and the sale does not need to be reversed; for ignorance of a prohibition is excusable, and the repentance of an ignorant person obliterates what preceded it, as mentioned by Ibn Taymiyyah.