Who needs an FEI number?

Can you tell me, who exactly requires an FEI number? Is it a necessity for all individuals or businesses involved in cryptocurrency transactions? Are there specific types of transactions or activities that necessitate the use of an FEI number? Are there any exceptions to the rule? And if so, what are the criteria for exemption? Additionally, how does one acquire an FEI number, and what are the potential consequences of failing to comply with this requirement? I'm eager to understand the specifics behind the need for an FEI number in the world of cryptocurrency and finance.