Is one who sold smartwatches based on an incorrect description conveyed to him sinful?

It is permissible to sell a commodity by description, and the buyer has the option to annul the sale or uphold the contract without compensation if the commodity turns out to be contrary to the description. This is called "the option of discrepancy in description." If returning the commodity is impossible due to its perishing, the buyer is entitled to compensation for the missing description.

If you relied on the mentioned description at the time of purchase without intending deceit, there is no sin upon you, but this does not negate the buyer's right to their option.

You can contact the buyers and inform them of the truth of the matter, giving them the option or compensation for the missing description. If they cannot be reached, it is best to give charity on their behalf equal to the value of the missing description from the price.