Sets the Social Security Number for a staff member who previously indicated they had applied for one but did not have it yet (applied_for_ssn = true). This action will re-render the current I-9 with the social security number and allows the I-9 to be processed through E-Verify.

Use the general Update Employee endpoint for ordinary profile changes. Use this endpoint for the deferred-SSN case, because only this path attributes the change to the staff member and triggers the full downstream I-9 flow.