What is the ruling on money acquired from buying and selling dollars and cryptocurrencies via mail, given the delay in receiving them and the presence of riba an-nasi’ah (usury of delay) in some transactions, and the questioner’s desire to dispose of the illicit money and pay off debt?

For currency trading to be permissible, it is a condition that there be immediate exchange (qabḍ) and no deferment. This exchange can be physical or constructive. If currency trading was conducted without observing the condition of immediate exchange, while knowing the religious ruling, then repentance to Allah is obligatory. As for past transactions and what was earned through them, it is hoped that you will be accommodated by the opinion of some scholars regarding the validity of your ownership of these funds, despite a difference of opinion on the ruling of owning what is acquired through a فاسد (invalid/corrupt) contract for someone who knows of its invalidity.