Click on this link to learn about 'Identity verification for Apple Card or Apple Cash' --> https://support.apple.com/HT207887
"To protect your account, you might be asked to verify your identity when using Apple Cash or applying for Apple Card."
"Why you'll be asked for your personal data
Person to person payments and the Apple Cash card are services provided by Green Dot Bank, member FDIC, a regulated financial institution. Green Dot Bank is required by federal law to verify the identity of its customers.
To verify your identity, Green Dot Bank will request social security numbers and other personal information to ensure that customers are eligible to use the service."