ORA-00913：嵌套大小的值过多

I am currently working on my first year assignment to build a database using Oracle Apex and am trying to create a report with fields to filter the table displayed. To do this using 2 parameters (in this case date of a dentist appointment and the staff member performing said appointment)I am using a nested case to check each field. I am getting the Error: I am currently working on my first year assignm