Enrollment Coverage start date issue in fast formula.

I have created fast formula as below and defined this rule under Program -->Timing-->Lifeevent-->New Hire -->Coverage-->Rule-->ARUP_OAB_UK_COVERAGE_DATE

This fast formula is not picking up the pl id and showing up the correct coverage start date. Can someone help me for this setup and correct me if I am wrong.

Type of fast formula : Enrollment Coverage Start Date

/*================ DEFAULT SECTION BEGIN=======================*/
DEFAULT FOR BEN_PLN_PL_ID IS 0
/*================ FORMULA SECTION BEGIN=======================*/

l_enrl_dt = ARUP_OAB_GET_ENROLLMENT_DATE('START')

If BEN_PLN_PL_ID = 71005 then

L_START  = ADD_DAYS(LAST_DAY(l_enrl_dt),1)