BitFuFu, a cloud mining company, has started a marketplace for discount coupons on the Antiminer branded rigs manufactured by Bitmain, the world's leading manufacturer of crypto mining machines.

Bitmain started issuing coupons for Antminers to loyal customers last year as sales slumped during the crypto market downturn. Many remain unused because miners are short on cash to spend on new equipment. Bankrupt companies including Celsius Network and Core Scientific (CORZ) have been trying to sell their coupons to raise funds that they can return to their creditors.

The platform opened Monday, BitFuFu, which is affiliated with the manufacturer, said in a statement shared with CoinDesk.

Ethan Vera, chief operating officer at mining services firm Luxor Technologies, estimates there are $50 million worth of coupons circulating in the market, and multiples of that will become available soon.

The coupons have value: Last week CleanSpark said it used some to lower the price of 20,000 machines by 26%.

BitFuFu has been planning to list on public markets via a special-purpose acquisition vehicle. It recently delayed its offering to May.

Read more: Cloud Mining Firm BitFuFu to Delay SPAC IPO as Appetite for Crypto Stocks Languishes