ISU_SIMULATION_PERIOD_BILL for grouped installation

Hi,

We have configured installation grouping data exchange as below:

For Secondary to Primary: ZQUAN_MPRN -> ZSUPP_SITE

For Primary to Secondary: ZSUPP_SITE-> ZTOT_SITE

We always bill the primary installation before the secondaries.

And we use the operand ZTOT_SITE for calculations when billing the secondary.

The problem is, when we perform billing through EA00/EAMABI, the operand is filled with the correct values and the calculations are correct.

When we use the FM ' ISU_SIMULATION_PERIOD_BILL' the operand has 0 value.

Is there anything we are missing.

We call the FM with the below parameters:

X_VERTRAG = The correct ISU contract

X_BEGABRPE = 01.07.2015

X_ENDABRPE = 31.07.2015

X_BILLINGRUNNO = 1

X_NO_UPDATE = X

X_SIMULATION = 06

Any input will be much appreciated.

Thanks.