How to get the start date of a payroll period using the coverage start date

Summary:

Rate Start Formula: START_DATE of the payroll period containing the coverage start date.

Content (required):

I'm attempting to use the BEN_FN_GET_CHAR_VALUE function for the PAY_TIME_PERIODS table to return the start date of the payroll period. I'm first calculating the coverage date (l_cvg_start_dt), and using it in parameter 6. I've tried different versions of the formula, some of which compile but all are returning one error or another. The current formula version fails to compile. I'm receiving the error message: Formula FAY_NEW HIRE RATE START DATE, line 27, either function BEN_FN_GET_CHAR_VALUE doesn't exist or the combination of parameter types doesn't match the statement.