statement contains an item of the wrong type in FF compilation

Summary:

I am using the following code in the fast formula and when fast formula is compiled it is giving a error message stating " statement contains an item of the wrong type."

P_ASG_ID is the assignment id and l_st_day is a date , can someone point where or what i have done incorrectly.

Content (please ensure you mask any confidential information):

GET_VALUE_SET('ATG_FlexBen_unpaid_abs', '|=P_ASG_ID='''||l_hr_asg_id||''''||'|P_DATE='''||to_date(l_st_day)||'''')

Version (include the version you are using, if applicable):