When you set up a new employee in Payroll, you should enter their Real Time Information (RTI) ID. This is used to capture the unique employee reference for your company, which is included in your submissions to HMRC.
If you’re transferring from another payroll system part way through a tax year that uses RTI Pay IDs, you must enter this when you set up the employee in Payroll. If you used HMRC Basic Tools, you can find the RTI Pay ID under Employee Details, then click Employment Details then look at the Payroll ID.
If your employee is a new starter who has moved from another business, or you haven’t previously used a payroll system to submit your employees under RTI, Payroll automatically assigns them an RTI Pay ID when you submit a full payment submission (FPS).
If an employee has already been included on a submission with a different software it is important that the same RTI Submission ID is used so that it prevents any duplicate profiles for this employee being created by HMRC.