Payment date is entered while you e-file the RTI FPS data to HMRC.It should be taken care that you enter the appropriate payment date.If you have not entered an appropriate payment date you will encounter the following errors.
1) In case of late e-filing,an important note and alert warning is displayed.You can then confirm late e-filing with Sign In password and select the proper "Late PAYE Reporting reason".
Please Note: It is very important that you select the correct reason for late e-filing so that it will help HMRC to determine whether any late filing penalties are due.
2) You are not allowed to enter the PAST/HISTORIC PAYMENT DATE prior to PAY PERIOD START DATE.
Scenario: For example, your current pay period month is 5(01-08-15 to 31-08-15), and you are doing late e-filing for pay period month 2(01-05-2015 to 31-05-2015). In this scenario you are not allowed to enter the payment date prior to the 01-05-2015(PAY PERIOD START DATE). The past payment date should fall on or after the pay period start date(within the tax year).