BAPI_CUSTOMERCONTRACT_CHANGE - billingplan identifier ?

Hi,

I´m using BAPI_CUSTOMERCONTRACT_CHANGE to change the end of contract(item) and the reason for rejection with success.

However there is a checkbox called "header" in the billingplan tab and I don´t know how to uncheck it via the BAPI.

What is the reason behind this checkbox ? I came across cz the only way to change the end date via the transaction is to remove the checkbox. But with the BAPI it´s no problem .

Any ideas ?