Issue to use expression rule in timer settings

Hello team,

i would like to use an expression rule in timer to define the day when a PM will run based on the values in DB. Every month the cut off day for processes is different and its defined in the DB. The expression rule which i call inside the timer is: =rule!ICH_getCutOffDataByFilters(    year: year(today()),    month: month(today())).day, and it simple calculate the cut off day for current month. But when i publish the PM i am receiving the following error message: ERROR:EVAL:@reason=Expression is invalid (1 token(s) remain after parsing)

Any advice please? Thanks