SSN is a secure field in the Finch API. Your use case needs to be approved by your Developer Success Representative before enabling. However, you can test SSN via the Finch Sandbox without any approval.
ssn product scope (along with individual) must be included in the /authorize URL when launching Finch Connect. This ensures that the connection’s access tokens that are generated are capable of accessing this field.
Authorization
Make sure to include thessn scope in your authorization URL.