Issue while developing a planning algorithm

I am trying to develop a algorithm using PDDL. Below here I am trying to define the domain and the problem files

Domain File:
(define (domain sp)
 (:requirements :typing)


 (:types    location agent item - object 
            robot human - agent 
            room - location
            fruit cup table - item)

(:predicates    
        (at ?o - object ?l - location)
        (detected ?p - human  ?l - room)
        (greeted ?r - robot ?p - human)
    )



    (:action detect
        :parameters (?p - human ?i - item ?r - robot ?l - location)
        :precondition (at ?r ?l)
        :effect (and (at ?p ?l) (at ?r ?l))
    )


    (:action greet
        :parameters (?r - robot ?p - human ?l - location)
        :precondition (and (at ?r ?l) (detected ?p ?l)) 
        :effect (greeted ?r ?p)
    )
)


Problem File:

(define (problem test12)
(:domain sp)

(:objects person0 - Human 
          pepper0 - Robot 
          apple - Fruit
          cup0 - Cup
          table0 - Table
          room0 - Room)

(:init
(at pepper0 room0)


)
(:goal (and 
        (detected person0 room0)
        (greeted pepper0 person0)
        )
)
)

What I am trying to achieve is

1. Robot is in the room
2. When human enters the room, robot needs to detect human
3. Greet human
4. The it has to detect other objects in the room (like cup, fruit, etc.)

When I run this code I am going to the following error.

solution-impossbible

ff: parsing domain file
domain 'SP' defined
 ... done.
ff: parsing problem file
problem 'TEST12' defined
 ... done.


ff: goal can be simplified to FALSE. No plan will solve it

I followed the syntax correctly but it throws this error. I am not sure how to go about it. Can anyone show me a direction and if possible some debugging resources for PDDL?

the output per-se is not an error. It simply indicates that there is no plan to your problem. The issue is that (detected ?p ?l) is never added by any action and is not in your initial state, so you will never be able to achieve it. You probably want to add it as an effect of the detect action (instead of (at ?r ?l)?).