They pleaded to conspiracy to run an unlicensed money transmitting business.
FinCEN told them they did not need a license and did not have a process in place to allow non-custodial entities to get a ...
They charged a fee to route through their servers. Other people transmitted money on their servers. This is the legal grey area... Sure they didn't transmit any money themselves, but their servers coordinated other people transmitting money. It's only a step removed. They should have never been public about it. They should have remained anonymous.
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