Field help (PAYDAY) 

This field can be accessed if the MAXPD - Maximum period (companies) activity code is activated.

It is relevant only if the BP is a private sector company, not a public sector organization.
In this case, you can have an agreement with this BP and grant them a longer period for the last payment due date than the period defined in the DMAXPAY - Maximum period (companies) parameter (TC chapter, RSK group).
Enter the contractual period in this field.
This period cannot exceed the period imposed by the current legislation and specified in the DMAXAGR - Maximum contractual period parameter (TC chapter, RSK group).