Hi,
The FM is checking whether PI document is counted. If yes, It gives error like below:
LK 036
Check your entries. Inventory count already complete or not available
I checked the LI12N transaction and FM itself. Both of them use FM L_ZAEHLUNG_BUCHEN to change quantity. So I think, I should use this also, or I can copy L_INV_COUNT_EXT and make Z FM.