i am getting the following error on my trigger
[Warning] ORA-24344: success with compilation error
3/62 PL/SQL: ORA-00904: “PEOPLE”.”FLATNO”: invalid identifier
3/9 PL/SQL: SQL Statement ignored
7/66 PL/SQL: ORA-00904: “PEOPLE”.”FLATNO”: invalid identifier
7/9 PL/SQL: SQL Statement ignored
(2: 0): Warning: compiled but with compilation errors

my trigger:

SET SERVEROUTPUT ON;
CREATE OR REPLACE TRIGGER TUTU
BEFORE INSERT OR DELETE OR UPDATE ON PEOPLE
FOR EACH ROW
BEGIN
IF INSERTING THEN
UPDATE FLAT SET Status = ‘Hired’ WHERE FLAT.FLATNO = PEOPLE.FLATNO;
END IF;

IF DELETING THEN
    UPDATE FLAT SET Status = 'Not Hired' WHERE FLAT.FLATNO = PEOPLE.FLATNO;
END IF;

END;
/

my tables:

CREATE TABLE FLAT(
FlatNo NUMBER,
Rent NUMBER,
FlatSize VARCHAR(20),
FlatType VARCHAR(20),
Facing VARCHAR(15),
RoomsNo NUMBER,
BuildingNo NUMBER,
Status VARCHAR(20),
PRIMARY KEY(FlatNo),
FOREIGN KEY(BuildingNo) REFERENCES BUILDINGS(BuildingNo)
);

CREATE TABLE PEOPLE (
PeopleID NUMBER,
Members NUMBER,
Paid NUMBER,
Due NUMBER,
HireDate VARCHAR(15),
Contact NUMBER UNIQUE,
FlatNo NUMBER,
PRIMARY KEY(PeopleID),
FOREIGN KEY(FlatNo) REFERENCES FLAT(FlatNo)
);