There are two elements to RTI:
Full Payment Submission (FPS):
Must be submitted by an employer every time they make a payment to an employee and must be sent to HMRC on or before the payment date.
Employer Payment Summary (EPS):
Only required to be submitted if there are any adjustments to the totals reported on the Full Payment Submission, i.e. statutory payment reclaim, Employment Allowance or Apprenticeship Levy. The EPS must be filed with HMRC on a monthly basis and the deadline is the 22nd of the month following the payroll (i.e. when payment is due).
The EPS is also used to inform HMRC if no payments are due for the month.