Clarification on RLS policy

We are presently using Postgresql:PostgreSQL 15.12 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-23), 64-bit

I have a scenario where

1.I need to enforce RLS policy on a table for Select by calling a Function

2.The function would return a character varying string which should be appended to the select as a filter.

Ex: Select * from employee would be appended with where 1=1;

3.When we try to implement it says the below error.