Xiang Shan knew why he had been caught. He had just been shopping in the Black Market, using nothing but digital currency.
This was uncommon in this era.
The most important reason was that, because digital currency at this time wasn't pegged to any sovereign state's legal tender, nor could any capital force speculate on it. Despite having a status akin to ancient "precious metals," the actual purchasing power of a single unit of digital currency wasn't very large.
At least in this era, "mining" was not a good choice.
The so-called "mining" of digital currency involved downloading certain data, then performing specific rule-based calculations and uploads, packaging it into blocks. The principle of digital currency was based on a "public ledger" called the "blockchain."