Reference element missing for token

Hello experts,

I am new to workflow.

I work on EWM system 9.1, where I am trying to create workflow condition to schedule PPF for delivery.

Workflow container has method GET_MO_BO() which returns table of items; one of the column is another object "ITEM", which has method GET_STOCK(), which returns stock category value.

Below is expression string, where I want to access the first line of table ITEMS, to read the column ITEM and to use the method for reading stock category.

&BUSINESSOBJECT.GET_MO_BO().ITEMS[1].ITEM.GET_STOCK().STOCK_CATEGORY&

However system returns an error message:

Reference element missing for token with index '10'

SWF_EXP_001 221

What is please the correct syntax for using multiple methods in one expression?

I would like to avoid programming.

Any help appreciated.

Thanks.

Petr