SSN basically required for federal anti-money laundering and anti-tax evasion regulation. It is mandatory due to a law. Having such type of information, it becomes useful for Cash app support team to trace any illegal transaction. SSN is basically created by the users, and you have to provide only the last four dodgers of it. To know more, take the Cash app help. https://www.7qasearch.net/cash-app-customer-service-phone-number/