Where does the Taliban get its money from?

The Taliban is megarich. Despite being out of power for 20 long years and losing tens of thousands of its members during a conflict with the West, it has grown rather rich and powerful in recent years. The insurgency group is believed to make over $1 billion each year through various sources. But, where does all that money come from?

source https://www.newsbytesapp.com/news/world/where-does-the-taliban-get-money-from/story