niNumber

The employee’s National Insurance number is an optional field in the /contributions request, but it is required by law within six weeks of the employer receiving it. Only valid National Insurance numbers will be accepted and recorded for an employee.

Temporary (starting with ‘TN’) and invalid National Insurance numbers are not accepted, though we treat this as if the National Insurance number was blank rather than returning a validation error.

The value provided (if any) will be returned in the /accounts/…/opt-outs response if the employee opts out of the scheme; it can be used along with uniqueId to match against employees in the payroll.