Individuals must report annually on foreign financial accounts if balances exceed a threshold amount. The question raised is whether these balances include cryptocurrencies. The Financial Crimes Enforcement Network may change the rules to specifically include these digital currencies. But instructions to FinCEN Form 114 for 2020, which is due April 15, 2021 (with an automatic 6-month extension) make it clear that cryptocurrency is not factored into balances as yet (https://www.fincen.gov/sites/default/files/shared/FBAR%20Line%20Item%20Filing%20Instructions.pdf).
Reporting income when actually or constructively received and deducting expenses when paid. Certain businesses may not use the cash method.