Please Note: Granted, what follows may very well not be possible with present technology, but I am discussing this from a perspective of fiction which is set some decades in the future.
 That said, this idea might well already have happened in reality for all we know.

 In pretty much any Cyberpunk-style universe, the focus is usually on the folks who live below the waterline of society.
 EG; Black and Grey market buyer/seller types, private enforcers and killers, hackers-for-hire and the rest.

 These are not people who will have anything to do with anything that might have the potential of being used to track them and who also have a genuine need for Hard Currency.
 This creates a real problem for writers, one that Crypto is helping solve...gotta love this technology as it's even helping solve problems in entirely fictional realities without having to resort to 'Handwavium' nonsense.
 Granted as a writer you often have to make extrapolative-leaps, but I like to keep things grounded in Plausibility as much as I can.

 So, do the underworld types go to a Barter System? Really unlikely except for the odd occasion where it works out due to sheer circumstance.
 Gold bars and such? Possible, but damned heavy and assorted other problems with it.
 What's an underworld economy to do?

 You create a 'MetaCoin'; A 'Greycoin' otherwise a Crypto token/coin that;
1; Operates 'anonymously' like Monero.
2; It operates on a split Proof-of-Work and Proof-Of-Stake protocol.
3; It would be a token/coin whose value is tied to the Market Average of all Cryptocurrencies in the 'Legitimate' market.
4; Then, you use an advanced 3D printing process to create bills/coins with microholographic information encoding on ribbon-like 'threads' throughout the bill/coin that act like akin to the way coin/token data is stored in a Cold Wallet or paper printout.

 That coin or bill is it's own value and cold-wallet, not merely a 'representation' of value like Fiat currencies.
 Phone apps (easily made) can be created for fast-scan authenticity verification vs. counterfeiting.
 Anyone can engage in creating this Hard Grey Currency, as counterfeits would be spotted quickly and as we are talking about the underworld, the punishment for such would be swift and final.

 Exchanging such 'greycoin' to be able to access legitimate market resources (like buying food at a fast food place) would be really easy through shadow exchanges that again would operate honestly or face some terrifying retribution.
 With the growth of A.I. tech, such exchanges could be entirely autonomous, cloud-based and 'roving', watched over by 'bodyguards' of netrunners as well as being equipped with constantly-updating anti-intrusion anti-hacking defenseware...some of which could well be 'Black ICE' or lethal-level anti-intrusion defenseware.

 Alternatively, that same exchange could be absolutely decentralized and cloud-roam across every system and smartphone there is...always available, extremely fast, and impossible to 'find'.

 Masternodes and such for this 'Greycoin' would be again absolutely decentralized, likely cloud-based, and 'roamware' that might very well use some variant of 'mixer' technology to 'piggyback' on mainstream crypto going through legitimate masternodes as well.

 More and more dust is coming off the old Cyberpunk works of mine, I'm doing some updating, lots of editing, touch-ups on character development which all brings it step-by-step closer to being Published.
 The above crypto idea solves the biggest problem the story had and which was responsible for my shelving it a few years ago.

Thank-You for Reading!!