For the year $2017,2018,2019$ and $2020$ the state of Gotham imposed a processing tax of $2\mathrm{.}5\%$ on all sales of cannabis made from medical dispensaries. HII Medical Dispensary collected the tax and paid it over to Gotham.$$ At the same time, it had begun litigation against the imposition of the tax as being unconstitutional. In $2021$ the Gotham Supreme Court found the tax to be unconstitutional.$$

Gotham offer HII Medical Dispensary a refund of the unconstitutional tax. HII received a refund of $$30,000.$ While HII$$s records were accurate, because of various circumstances, HII was only able to refund $$20,000$ to customers who has paid the tax.$$

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Assuming the refund to the customers are deductible when can HII deduct these payment?$$