After all, buying things from Otherworld itself incurs hefty tariffs, the more luxurious the item, the more high-tech, the heavier the tax.
Moreover, there was another problem. If Li Pan took this money to buy cars and houses, enjoying himself would be one thing, but if he went to buy military equipment, Mecha SMS, and the like, the moment he went out on missions to Grass Valley, people would see, "Hey, isn't this registered in the name of the Monster Company? Quick! Call the police!" What then...?
As for setting up a bank account in a border plane to launder money, that was also not feasible, just forget about it.
Yes, Li Pan indeed had eighteen million in Black Money that he couldn't launder, but paying someone to launder it and laundering it himself were two different things in nature.
If the former happened, at most he would receive criticism and re-education, but the latter would have the tax bureau's fleet jumping to capture him.